A suicide attacker detonated explosives packed into a vehicle in front of a police academy in northern Iraq Saturday as scores of recruits were leaving the compound, killing at least 15 policemen and wounding 36 people, the U.S. military said.

The blast at the police academy in Kirkuk capped a day of violence across Iraq. In the northwestern town of Tal Afar, near the Syrian border, an operation to capture leaders of a terrorist cell sparked intense clashes between insurgents and U.S. and Iraqi security forces that left nine Iraqis dead and 50 wounded.

Near the southern port of Basra, an attack on an oil pipeline reduced the flow of crude to export storage tanks. And in Baghdad, several mortar shells were fired in the direction of the convention center where Iraq's interim National Council was meeting.

Despite predictions Friday that insurgents would release two French journalists being held hostage, the pair remained in captivity. In Paris, France's interior minister insisted that signs still pointed to an imminent release, but he suggested that insecurity in the country was complicating the process.

"All the indications that we have confirm the hope of a release soon," Interior Minister Dominique de Villepin said. "But you know the situation that exists in Iraq and, in this context, the greatest caution is of course necessary."

The journalists, Christian Chesnot and Georges Malbrunot, were kidnapped Aug. 19 as they traveled from Baghdad to the city of Najaf.

In Kirkuk, witnesses and police officials described a tableau of tragedy that has become hauntingly familiar to Iraqis: bodies blown apart, bloodied survivors seeking medical attention and a street littered with mangled cars and broken glass. Twenty-four of those injured were police.

A senior police official, Shirku Shakir Hakim, said the suicide bomber had been waiting in a car in front of the academy for a large number of people to leave. When a passerby asked what he was doing, the driver responded that he was there to pick up someone, Hakim said.

In Tal Afar, soldiers with the 3rd Brigade of the U.S. Army's 2nd Infantry Division, a unit that uses the military's new Stryker armored vehicles, conducted a joint operation with Iraqi National Guard forces to apprehend a militant leader, the U.S. military said in a statement. Although the forces arrested the man , the operation touched off an intense insurgent counterattack involving small arms and rocket-propelled grenades, the military said.

Insurgent fire brought down an OH-58D Kiowa Warrior observation helicopter, injuring its two crew members. Twenty minutes later, a rocket-propelled grenade disabled a Stryker vehicle. The crew inside the vehicle, which is built to withstand grenade fire, was unharmed.

U.S. forces then called on an Air Force jet to bomb a concentration of insurgents near the city. Three Iraqi National Guard members were among the 50 injured, the military said.

Local officials interviewed by the Associated Press said many of the casualties were caused by a mortar shell, presumably fired by the insurgents, that hit a market.

In a statement, the military said Tal Afar "has been a suspected haven for anti-Iraqi forces crossing into Iraq from Syria."

The pipeline attack affected a feeder line near the town of Hartha, about 20 miles north of Basra. The pipeline carried 15,000 barrels of crude a day from the Nahran Omar oilfields to an export storage tank, according to the AP. Officials with Iraq's state-run South Oil Co. could not be reached for comment.

Iraq's interim government said late Saturday that it would extend its closure of the offices of al-Jazeera, an Arab satellite television network. The government had shut down al-Jazeera's offices on Aug. 5 for one month after a government committee concluded that the network's broadcasts incited violence.

The government national security committee said in a statement that it had decided "to extend the suspension of the channel's activities from Iraq until the station comes forward with a written explanation specifying the motives behind its policy toward Iraq."

In a statement, al-Jazeera said, "This decision runs contrary to pledges made by the Iraqi authorities to pursue a policy of openness and to safeguard freedoms of the press and expression."

The interim prime minister, Ayad Allawi, insisted in a recent interview that the government committee that recommended the initial shutdown of the station "illustrated beyond the shadow of a doubt that al-Jazeera is helping the terrorists."

"You may not like it, but this is the facts," he said.

Special correspondent Marwan Ibrahim in Kirkuk contributed to this report.

The bomber waited for recruits to leave a police academy in this vehicle, now reduced to a charred hulk.