ODESSA, Ukraine — Talks between Russian and Ukrainian officials ended without a breakthrough Monday, and safe passage from cities under attack remained elusive, as the 12-day-old war continued to create a humanitarian catastrophe.

Ukrainian cities including Kyiv, Kharkiv, Chernihiv, Mykolaiv and Mariupol are under bombardment, and some civilians are being hit as they attempt to flee, according to a senior U.S. defense official who spoke on the condition of anonymity under terms set by the Pentagon. The official cautioned that the United States could not say with authority whether those civilians were being targeted intentionally.

Ukrainians cross a damaged bridge on the outskirts of Kyiv as they flee the capital Monday. Heidi Levine/The Washington Post

Efforts to establish evacuation corridors for noncombatants have faltered in recent days, even as the onslaught has left hundreds of thousands of residents without water, heat or natural gas. Ukraine accused Russia of disrupting two previous attempts to allow civilians to leave over the weekend and allow much-needed supplies to be brought in. On Monday, the government rejected a proposal by Moscow to move residents of besieged cities toward Russia.

“Just cynicism, just propaganda,” was how Ukrainian President Volodymyr Zelensky described Russia’s talk of “humanitarian corridors.” He reiterated his call to establish a no-fly zone over Ukraine to counter the Russian assault, saying his country has been thrust into suffering “that no other European nation has seen in 80 years.”

North of Kyiv, the capital, the booming thud of artillery fire sent civilians fleeing for cover Monday as parents with children and the elderly tried to cross the Irpin River, away from advancing Russian forces.

In Odessa, a major port and cultural hub on the Black Sea, Mayor Gennadiy Trukhanov said he expected a possible Russian attack from the east, where Moscow’s forces have already captured the city of Kherson, and from a group of Russian warships just outside Ukraine’s territorial waters. “The aggressor is not far,” warned Trukhanov, who said he was keeping a loaded pistol at his side at all times.

More than 400 civilians have been killed and 800 injured since the war began on Feb. 24, according to the United Nations, although those figures are probably a considerable underestimate because of delays in corroborating information. At least 1.7 million refugees from Ukraine, half of them children, had arrived in neighboring countries as of Sunday, said Catherine Russell, the executive director of UNICEF.

The World Health Organization has confirmed 14 attacks on health-care facilities and personnel in Ukraine since the war began.

In Washington, a bipartisan group of lawmakers announced Monday that they had reached a deal on a bill that could ban U.S. imports of Russian oil and further empower President Biden to levy tariffs on Russian goods. Biden conferred with the leaders of France, Germany and Britain on developments in Ukraine, the White House said in a statement, and the leaders remain determined to “continue raising the costs on Russia for its unprovoked and unjustified invasion.”

Efforts to inflict pain on Russia are likely to have broader economic consequences, particularly on the price of energy. On Monday, the price of oil briefly jumped to a 14-year high of $139 a barrel before retreating, and U.S. financial markets fell sharply. European leaders said they plan to reduce their reliance on Russian energy imports but did not want to commit to an immediate ban.

People cook outdoors for the Ukrainian servicemen and civil defense members serving in Kyiv, Ukraine, on Monday. The United Nations is unable to meet the needs of millions of civilians caught in conflict in Ukraine today and is urging safe passage for people to go “in the direction they choose” and for humanitarian supplies to get to areas of hostilities, according to the U.N. humanitarian chief. (AP Photo/Vadim Ghirda)

“Obviously, there’s a lot of debate going on about energy sanctions,” Dutch Prime Minister Mark Rutte said at a news conference Monday. “Here, we should not make a mistake. We have to ensure that they don’t generate unmanageable risks to energy supplies in European countries and beyond.”

Meanwhile, Moscow is attempting to recruit fighters from Syria to help fuel its war effort, the senior U.S. defense official said, as “nearly 100 percent” of the Russian troops who were pre-positioned around Ukraine already have been sent into the country to fight.

The official said there was no indication that Moscow was preparing to dispatch additional Russian forces to supplement the 127 battalions that were staged around Ukraine before the invasion. The advance of those units has been selectively slowed and blocked by logistical problems and Ukrainian resistance. Instead, the official said, Russia appears to be increasing its bombardments of population centers and using long-range missiles.

The Pentagon has tracked more than 625 Russian missile launches since the fighting began. Initially, most of those consisted of short-range projectiles, but now such missiles “are no longer the majority,” the official said.

In Belarus, a third round of talks between Russia and Ukraine finished without progress toward ending the conflict. Ukrainian negotiator Mykhailo Podolyak said the talks produced some headway toward logistical arrangements for local cease-fires and evacuation corridors after several days of failed efforts. Still, “as of today, there are no results that significantly improve the situation,” Podolyak said.

The head of the Russian delegation, Vladimir Medinsky, said he hoped there would be progress in a fourth round of talks in the coming days and that humanitarian corridors would begin working Tuesday.

Refugees fleeing the military operation zone, from the Mariupol area of Ukraine sit on a bus as they arrive at the border crossing in Veselo-Voznesenka, Russia, Monday. Russia announced yet another limited cease-fire and the establishment of safe corridors to allow civilians to flee some besieged Ukrainian cities. (AP Photo)

The foreign ministers of Russia and Ukraine are scheduled to meet in Turkey as early as Thursday, their first meeting since Moscow’s invasion began, Turkey’s foreign minister announced Monday. Other parties have also recently offered to act as potential mediators in the conflict, including China and the Vatican.

The Kremlin has demanded that Ukraine surrender a large slice of the country’s east and acknowledge Crimea as part of Russia as conditions for ceasing hostilities. Russian President Vladimir Putin has also insisted that Ukraine demilitarize, declare neutrality and give up any bid to join NATO.

U.S. Secretary of State Antony Blinken visited Lithuania on Monday, as part of a European tour aimed at illustrating Western unity against the Russian invasion. As he welcomed the top U.S. diplomat, Lithuanian President Gitanas Nauseda warned that Putin may “not stop” his territorial expansion if he successfully captures Ukraine.

The Pentagon said it will send an additional 500 troops to bolster the U.S. presence in Eastern Europe, a deployment that includes KC-135 tanker planes that will be based in Souda Bay, Greece, and forces that will establish an air operations center in Romania and Poland. The forces will join more than 12,000 troops that have deployed since Russia began massing its forces outside Ukraine’s borders. Biden has said the troops will not fight in Ukraine.

Ukraine has opened a proceeding at the United Nations’ top court in The Hague seeking an immediate end to the fighting and has dispatched teams to gather evidence at bombed sites for possible future war crimes prosecutions. The case centers on Russia’s official explanation for its invasion of Ukraine, which Putin has said is intended to achieve the “denazification” of Ukraine and end a “genocide” in the country’s east. There is no evidence to support Russia’s claims. Representatives of Ukraine reiterated Monday that the Russian accusations are false and represent a pretext for an illegal invasion. Russia did not appear at a hearing in the case Monday, effectively boycotting the process.

On Monday, Russia’s Defense Ministry announced the formation of six evacuation corridors, including three leading to Russia and one to Belarus, a close ally of Moscow. Ukrainian Deputy Prime Minister Iryna Vereshchuk called the offer “unacceptable,” insisting that the flow of people from battle zones should be allowed into western Ukraine or European Union countries.

French President Emmanuel Macron accused Putin of hypocrisy and said the plan for the corridors was “not serious.” “It is moral and political cynicism,” Macron said in an interview with a French news channel.

In Mariupol, a city in southern Ukraine, an estimated 200,000 civilians remain under siege. Residents are without heat, they lack access to basic supplies such as food and medicine, and the water system has broken down, said Anton Gerashchenko, an adviser to the Ukrainian government, on Facebook.

About 1 million consumers in southeastern Ukraine will be cut off from natural gas – a key source of heating and cooking fuel – after Russian shelling damaged a main pipeline, according to the country’s Gas Transmission System Operator. A huge swath of people in southeastern Ukraine – in the regions of Donetsk and Zaporizhzhia – “will be left without a gas supply,” it said in a statement.

The exodus of multinational companies from Russia continued Monday as firms face pressure from employees and customers to repudiate the war. Ernst & Young, a major global accounting firm, announced that it would wind down operations in Russia, calling the conflict in Ukraine “shocking and abhorrent.” Deloitte, another of the “Big Four” accounting firms, said it would also exit the market, following similar announcements by PricewaterhouseCoopers and KPMG on Sunday.

Aviation giant Boeing has stopped buying titanium from Russia, a company spokesperson said, adding to a widespread boycott by Western business that threatens to leave Russia economically isolated for years. Boeing uses Russian titanium in its 737, 767, 787, 777 and 777x airplanes for items such as fasteners, landing gear and flight-control structures.