A parked car bomb exploded in a residential district of Kirkuk on Saturday, killing four people and injuring another 13, police said. The U.S. command said three U.S. Marines died in action in western Iraq.

The bombing occurred around 2 p.m. in the al-Wasiti district of Kirkuk, about 180 miles north of Baghdad. It was the sixth car bombing this month in Kirkuk, where tensions are rising among Arabs, Kurds and Turkomen for control of the area's vast oil wealth.

Also Saturday, the western regional commander of the Iraqi Border Protection Force, Brig. Gen. Jawad Hadi al-Selawi, was killed in Karbala, 50 miles south of Baghdad, police said.

Sectarian violence has escalated in Iraq in recent months, with Sunni radicals — including members of Al Qaeda — and Shiite militias staging tit-for-tat killings. Thousands from both sects have fled the country, according to Iraqi officials.

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Gunmen in two cars sprayed gunfire at the Muhammad Rassulluallah mosque in western Baghdad shortly after midnight, shattering its windows and damaging walls, police said. One guard was injured.

The Marines died Thursday in Anbar, the western province that is a focal point of the Sunni-dominated insurgency. A U.S. statement said they were attached to the Army's 1st Armored Division, which operates in Ramadi, but gave no further details.

Their deaths brought the number of U.S. service members who have died since the beginning of the Iraq war in March 2003 to at least 2,573, according to an Associated Press count. The figure includes seven military civilians.

In Baghdad, six day laborers were wounded when a bomb exploded downtown in Tayaran Square, where the workers had gathered to wait for jobs. Three policemen were also wounded when a roadside bomb struck their patrol in northern Baghdad, police said.

A Sunni cleric from a tribe opposed to Al Qaeda in Iraq was killed while driving in Samarra, about 60 miles north of Baghdad, police said.

And in Fallujah, four including one policeman were wounded in an mortar and rocket-propelled grenade attack, police said.

Iraq's national soccer coach also resigned after receiving a death threat, sporting officials said. The country's wresting coach was killed July 13. Two days later, more than 30 sporting officials, including the chairman of Iraq's Olympic Committee, were seized during a meeting in Baghdad.

At least 10 of them have been freed, but dozens are still missing, including National Olympic Committee chairman Ahmed al-Hijiya.

The attacks came a day after the head of the biggest Shiite party called for a greater security role for Iraqis in the country in place of Americans. The remarks by Abdul-Aziz al-Hakim run counter to U.S. plans to put more American soldiers on the streets of Baghdad to try to curb the surge in sectarian violence.

The U.S. plan calls for moving up to 5,000 additional American troops with armored vehicles and tanks into the capital. Some critics believe the move will undermine confidence among Iraqi forces and expose more U.S. soldiers to attacks by Sunni insurgents and Shiite militias.

Al-Hakim, the former commander of the feared Badr Brigade militia, has long complained the Americans have interfered with Iraqi forces' efforts to crack down on Sunni insurgents and Al Qaeda in Iraq terrorists. He said the surging violence was due to "being lax in hunting down terrorists and upholding the wrong policies in dealing with them."

Al-Hakim said Sunni extremists and Saddam Hussein loyalists were to blame for the violence.

However, he also endorsed the government's pledge to disband militias, including those affiliated with Shiite politicians.

Members of al-Hakim's Supreme Council for the Islamic Revolution in Iraq have been suspicious of U.S. and Iraqi government peace overtures to Sunni insurgents and have privately complained that top Sunni politicians have intervened to free detainees in Baghdad.

Al-Hakim's speech marked the third anniversary of the death of his elder brother, Ayatollah Mohammed Baqr al-Hakim, who was killed by an Al Qaeda-linked car bomb attack in Najaf.

Also Friday, another top Shiite politician, Hadi al-Amiri, said there were rumors of a plot to overthrow the government of Prime Minister Nouri al-Maliki, a Shiite, and replace it with a secular "government of national salvation." He did not elaborate.

"We don't call it a national salvation government, we call it a military coup," said al-Amiri, leader of the Badr Brigade militia. "We'll prevent that because that means canceling the constitution and the results of the elections and entering a dark tunnel, which is something we will never allow."