BAGHDAD, Iraq – A suicide attack and roadside bombings killed six American soldiers, and Iraq’s prime minister warned residents of insurgent bastion Fallujah yesterday to hand over terror mastermind Abu Musab al-Zarqawi or face military action.

Mr. al-Zarqawi’s Tawhid and Jihad group has claimed responsibility for beheading several foreign hostages and for car bombings throughout the country, and a videotape posted yesterday on an Islamic Web site showed terrorists linked to Mr. al-Zarqawi beheading two Iraqis they accused of being intelligence officers.

The attacks, at a time when American forces are putting pressure on insurgent strongholds in the Sunni heartland, occurred in the run-up to the Islamic holy month of Ramadan, which Iraqi TV said would begin here Friday. Some extremists believe they earn a special place in paradise if they die in a jihad, or holy war, during Ramadan, when Muslims believe God revealed their holy book the Koran to the Prophet Muhammad.

Iraq’s deteriorating security, including bombings, mortar and rocket attacks, kidnappings and shootings, has slowed reconstruction efforts and forced America to divert funds from rebuilding to security.

An assistant secretary of state, Richard Armitage, acknowledged that America was initially too slow in channeling money to Iraq, telling a donors’ conference in Tokyo that “it took longer than necessary to get our act together prior to turning over sovereignty” to Iraqis on June 28.

Yesterday’s suicide attack came when a driver plowed into an American convoy and blew up his car in the northern city of Mosul, killing two American soldiers and wounding five, according to the military. Four other soldiers were killed in roadside bombings in the Baghdad area – three late Tuesday and one early yesterday, the command said.

Last year, the advent of Ramadan was marked by a surge in insurgent attacks. To prevent a repeat, American troops have stepped up offensive operations in Sunni Muslim strongholds to the north and west of Baghdad.

More than 1,000 American and Iraqi troops launched two simultaneous raids yesterday around Baqouba, 35 miles northeast of Baghdad, to clear the area of insurgents.

“Basically, it’s a pre-Ramadan operation just to clear up some of the area around Baqouba,” said Captain Marshall Jackson, spokesman for the 3rd Brigade, 1st Infantry Division.

In an unrelated attack, a police captain was killed yesterday in a drive-by shooting near Baqouba, officials said. Insurgents regularly target Iraq’s security forces, who are seen as collaborators with America and its allies.

Elsewhere, American troops sealed off key streets and searched buildings in the insurgent stronghold of Ramadi, 70 miles west of Baghdad, after days of clashes, residents reported. The American command had no comment.

On Tuesday, Iraqi government soldiers backed by American Marine and Army units raided seven mosques in Ramadi, detaining four people and seizing bomb-making materials and pro-insurgent literature, the military said.

American and Iraqi authorities have used a mix of diplomacy and force to try to regain control of insurgent enclaves in time to hold nationwide elections in January.

But the major insurgent stronghold is Fallujah,a city of 300,000 that has become the symbol of Sunni resistance. American forces have staged weeks of “precision strikes” aimed at buildings believed to be safehouses of Mr. al-Zarqawi’s network and its associates.

At the same time, Iraqi officials have been negotiating with representatives of Fallujah to restore government control of the city, which fell under the rule of extremist religious leaders and their armed fighters after the Marines lifted their three-week siege last April.

Yesterday, Prime Minister Allawi warned that Fallujah must surrender terrorist leaders, chief among them the Jordanian-born Mr. al-Zarqawi, if they want to avoid attack. The Americans have insisted for months that Fallujah must hand over foreign fighters and those responsible for the brutal slaying last March of four American contractors, which triggered the siege.

“If they do not turn in al-Zarqawi and his group, we will carry out operations in Fallujah,” Mr. Allawi told a meeting of the 100-member interim National Council. “Fallujah of course is an honest city but it has been manipulated by a deviant bunch that wants to harm Iraq.”