BAGHDAD, Iraq (AP) – U.S. troops have sharply increased patrols in Baghdad since the spike in sectarian violence, a U.S. general said Thursday, raising questions about the capabilities of Iraqi forces. A car bomb killed least 15 people in a Shiite area of the capital.

At least 21 other people, including an American soldier and seven members of a Sunni family, were killed Thursday.

With sectarian violence on the rise in Baghdad, the U.S. command boosted the number of armed patrols in the capital from 12,000 in February to 20,000 since the beginning of March, Maj. Gen. Rick Lynch told reporters.

Lynch said the increase provides a “more visible presence for the security forces in the streets of Baghdad,” which he said insurgents consider their “center of gravity” to prevent a new unity government.

“We’re taking the fight to the enemy specifically in Baghdad with the presence we have on the ground,” Lynch said.

Tit-for-tat killings between Shiites and Sunnis soared after the Feb. 22 bombing of a major Shiite shrine in Samarra, triggering reprisal attacks against Sunni mosques and clerics. Violence was worse in religiously mixed areas of Baghdad, forcing the Americans to return to neighborhoods such as Shula that had been turned over to the Iraqis.

That casts doubt on the capability of Iraqi forces to deal with sectarian violence, despite assurances from American officials that the new army and police forces were gaining steadily in professional skills.

The renewed American presence has not been enough to stop the carnage. The car bomb exploded in a vegetable market in Shula packed with shoppers buying food for their evening meals, police said. At least 15 people were killed and 22 were wounded. Last week, a car bomb injured 13 people in the same neighborhood.

A roadside bomb Thursday killed a U.S. soldier southwest of Baghdad, the military said. The U.S. command also reported that a Marine died Wednesday of wounds suffered in hostile action near Baghdad.

More American troops were killed in the first two weeks of April – 37 – than in the entire month of March, when 31 died, according to an Associated Press count. At least 2,366 members of the U.S. military have died since the war started in 2003, according to AP.

Elsewhere, gunmen stormed the house of a Sunni family in Basra, 340 miles southeast of Baghdad, and killed seven people – a father, five of his sons and another relative, police said. A navy officer and his friend were killed by drive-by shooters while walking downtown in the largely Shiite city.

Late Thursday, insurgents ambused a convoy of Iraqi police enroute from Najaf to the U.S. base at Taji just north of the capital to pick up new vehicles, police said. Officials in Najaf said there were casualties but they had no figures.

In Baghdad, Mahmoud al-Hashimi, whose brother heads Iraq’s largest Sunni Arab political party, was slain along with a companion Thursday as they drove through a mostly Shiite area, the Iraqi Islamic Party said.

Tariq al-Hashimi is among the key players in negotiations over a new national unity government, which have stalled over the issue of who will be the next prime minister.

The Shiites, the biggest bloc in the 275-member parliament, have nominated Prime Minister Ibrahim al-Jaafari for a second term. But Sunni and Kurdish parties, whom the Shiites need as coalition partners, have rejected al-Jaafari and called on the Shiites to name a new candidate.

Al-Jaafari’s supporters within the seven-party Shiite alliance have refused to replace him, and other groups within the bloc fear that trying to force him out will shatter the Shiite political movement.

Parliament speaker Adnan Pachachi has called for parliament to convene Monday to try to resolve the crisis, but Shiite politicians are reluctant to attend until a deal has been struck on the premiership and other top government posts that require parliamentary approval.

Khudayer al-Khuzai, who supports al-Jaafari, proposed that leaders of major Shiite, Sunni and Kurdish parties meet Sunday to try to reach consensus on candidates for top jobs.

“If we don’t agree on the key posts, then why should we go to parliament?” al-Khuzai asked Thursday.

Voters chose the 275-member assembly on Dec. 15, but the legislature met briefly only once last month. The lack of progress has frustrated Iraqis, especially as steady violence – much of it sectarian – continues to claim hundreds of lives and threatens to push the country into a large-scale civil war.

Politicians echoed the discontent, chastising the top leaders’ failure to agree.

“There are some political blocs who’d rather just be in power than provide security to the people,” Sunni politician Saleh al-Mutlaq told reporters. “We demand the political entities speed up the formation of the national government and stop the bloodshed in Iraq.”

Separately, the U.S. military said four suicide – instead of the two initially reported – were behind last week’s deadly attack on a Shiite mosque that killed at least 85 worshippers in northern Baghdad.

The U.S. military said three male bombers made it inside the mosque complex in Buratha, and one believed to be a woman was just outside the entrance.

Lynch blamed the Jordanian militant Abu Musab al-Zarqawi, who heads al-Qaida in Iraq.

“His signature are these suicide attacks,” Lynch said. “We know he’s using those attacks to enflame sectarian violence.”

In other violence Thursday, according to police:

– Police in Basra found the bodies of two men who had just been kidnapped – an engineer and a translator working with British troops in the area. Another abducted engineer was still missing.

– A Foreign Ministry worker was kidnapped and a Health Ministry laborer was wounded in a shooting that killed her driver. A Housing Ministry employee also was wounded in a drive-by shooting.

– Gunmen killed a policeman who was driving his sons to school in Mosul. One of the sons also was killed and the other seriously wounded.

– Four other people were killed in random shootings in the Baghdad area and central Iraq.

—

Associated Press Writers Vanessa Arrington, Qassim Abdul-Zahra and Sinan Salaheddin in Baghdad contributed to this report.

AP-ES-04-13-06 1849EDT