MOSCOW — Russia’s top diplomat accused the United States on Wednesday of carrying out an unlawful attack against Syrian President Bashar Assad’s forces as he opened a fraught meeting with visiting U.S. Secretary of State Rex Tillerson.

Giving Tillerson a chilly reception, Russian Foreign Minister Sergey Lavrov said Russia was trying to understand the “real intentions” of the Trump administration. He said Moscow has lots of questions about the “very ambiguous” and “contradictory” ideas emanating from Washington.

“We have seen very alarming actions recently with an unlawful attack against Syria,” Lavrov said, referring to the cruise missiles President Donald Trump ordered to punish Assad for using chemical weapons. “We consider it of utmost importance to prevent the risks of replay of similar action in the future.”

It was an ominous start to Tillerson’s visit — the first to Russia by a Trump Cabinet official. Tillerson conceded the two world powers had “sharp differences” that have obstructed cooperation but voiced optimism that their talks could narrow those differences.

“We both have agreed our lines of communication shall always remain open,” Tillerson said.

Trump, meanwhile, told Fox Business News that the U.S. had no plans to become more deeply involved in Syria and only did so because of last week’s deadly chemical weapons attack that killed dozens. Turkey has said tests showed sarin gas was used.

“Are we going to get involved with Syria? No,” Trump said in the interview, which aired Wednesday in the U.S. “But if I see them using gas…we have to do something.”

The palpable tension hanging over Tillerson’s trip spoke to a widening chasm between the former Cold War foes.

Only weeks ago, it appeared that Trump, who lavishly praised Russian President Vladimir Putin throughout the campaign, was poised for a potentially historic rapprochement with Russia. But any expectations of an easy rapport have crashed into reality as the two countries trade escalating accusations over what happened last week in rebel-held territory in northern Syria.

“Frankly, Putin is backing a person that’s truly an evil person,” Trump aid in the Fox Business Network interview, referring to Assad. “I think it’s very bad for Russia. I think it’s very bad for mankind.”

Of Assad, Trump added: “This is an animal.”

And Putin, who U.S. intelligence agencies say tried to help Trump get elected, insisted that relations with the U.S. had only gone downhill since Trump took office in January.

“The level of trust at the working level, especially at the military level, has not become better but most likely has degraded,” Putin said in an interview broadcast Wednesday by state television channel Mir.

It was unclear whether Putin, who once gave Tillerson an “Order of Friendship” award, would grant the visiting American an audience. Though the Kremlin had declined to say whether the leaders would meet, Putin spokesman Dmitry Peskov said Wednesday: “There is a certain likelihood.”

Moscow has strenuously objected to Trump’s decision to launch 59 U.S. Tomahawk missiles at a Syrian air base that the U.S. says was used to pummel civilians with nerve gas, resulting in 87 deaths. Russia, Assad’s staunchest ally, has insisted that Assad is blameless and that it was actually the rebels responsible for the disbursed chemical weapons.

Intelligence services from several Western countries dispute that claim. The health minister in Turkey, which treated many of the attack’s victims and conducted autopsies on others, said Tuesday that test results conducted on victims confirmed sarin gas was used.

Adding further fuel to rising tensions: the White House’s move to circulate declassified U.S. intelligence accusing Moscow of aiding Assad’s government in covering up the chemical attack. The U.S. also accused Russia of mounting a disinformation campaign aimed at exonerating Assad.

Tillerson, on a mission to persuade Russia to abandon Assad, issued an ultimatum to Putin before flying to Moscow: Either side with the U.S. and likeminded countries, or with Assad, Iran and the militant group Hezbollah.

But Russia made clear it had no intention to acquiesce. Putin quickly invited the Syrian and Iranian foreign ministers to Moscow on Friday, the day after Tillerson departs.

“Our policy is consistent and it’s formulated exclusively on the basis of international law and not under the impact of current opportunistic motives or false choice: ‘You are with us or against us,'” Lavrov told Tillerson.

The Trump administration’s growing willingness to confront Russia directly is serving another purpose: defanging the perception of coziness between Trump and Moscow. As the FBI and multiple congressional committees investigate potential collusion between Russia and Trump’s campaign in last year’s U.S. election, Trump can point to his hard-line stance as fresh evidence that he’s far from beholden to the Russian leader.

Subtly mocking his guest, Lavrov said their talks were especially important because “not all key positions in the State Department have been filled yet.” He was referring to widespread vacancies throughout the top State Department leadership that has fueled a perception in the U.S. that Tillerson and his agency are being sidelined by Trump.

“It’s not easy to get clarifications on the current as well as prospective issues because of that,” Lavrov said.

Associated Press writers Vladimir Isachenkov, Nataliya Vasilyeva and Jim Heintz contributed to this report.

Russian Foreign Minister Sergey Lavrov, center, listens to US Secretary of State Rex Tillerson, right back to the camera, during their talks in Moscow, Russia, Wednesday, April 12, 2017. Tillerson’s Moscow talks hinge on new US leverage over Syria. US Secretary of State Rex Tillerson, left, and Russian Foreign Minister Sergey Lavrov shake hands prior to their talks in Moscow, Russia, Wednesday, April 12, 2017. Tillerson’s Moscow talks hinge on new US leverage over Syria. US Secretary of State Rex Tillerson, left, and Russian Foreign Minister Sergey Lavrov walk prior to their talks in Moscow, Russia, Wednesday, April 12, 2017. Tillerson’s Moscow talks hinge on new US leverage over Syria.US Secretary of State Rex Tillerson,right, and Russian Foreign Minister Sergey Lavrov, enter a hall prior to their talks in Moscow, Russia, Wednesday, April 12, 2017. Tillerson’s Moscow talks hinge on new US leverage over Syria.