BAGHDAD, Iraq - Insurgents shelled the heavily fortified Green Zone in central Baghdad early today, and U.S. and Iraqi commanders said more than 400 suspects were captured during an offensive to retake the northern town of Tal Afar.

Two mortar rounds exploded near a military hospital inside the protected area that houses the Iraqi government, parliament, and foreign missions, police said. There were no reports of casualties.

Security inside the Green Zonewas boosted earlier this month after reports that suicide bombers were trying to penetrate the area.

Meanwhile, U.S. commanders in Tal Afar said that more than 400 suspected rebels were in custody as a result of recent offensive there. The Iraqi military reported today that its troops had detained 36 more rebels, including a Yemeni citizen, just south of Tal Afar.

"Now, (the guerrillas) are just trying to save themselves by hiding in houses and communities," Col. H.R. McMasters, commander of the American contingent from the 3rd Armored Cavalry Regiment, said. "The enemy no long enjoys any kind of a safe haven or a support base in the city."

"This operation was very precise. We've had access to all the terrorist safe havens," said Brig. General Muhsen Yahya, commander of the Iraqi Army's 1st Brigade in Tal Afar.

On Monday, officials said the insurgent death toll in three days of fighting in Tal Afar totaled 200. Seven Iraqi soldiers and six civilians also died; the U.S. military said no American soldiers were hurt.

Prime Minister Ibrahim al-Jaafari flew to Tal Afar on Monday to congratulate his army, and Al-Iraqiya state television said he went despite insurgent threats "to attack the city with chemical and biological weapons."

There was no known public threat from the insurgents to use unconventional weapons in Tal Afar, but militants made two Internet postings in recent days vowing to stage chemical attacks on the Green Zone.

The Islamic Army in Iraq, which has previously claimed responsibility for kidnappings and killings of foreigners, made a bounty offer for the assassination of key Iraqi officials.

The militant group called in a Web posting for its "holy fighters to strike the infidels with an iron fist." It offered $100,000 to the killer of al-Jaafari, $50,000 for the interior minister and $30,000 for the defense minister.

Iraq's U.S.-trained forces and U.S.-backed government are waging their own media offensive, using the Tal Afar operation to position themselves as a confident and strong team leading the fight to wipe out insurgent forces.