Insurgents fired mortars after sundown Tuesday in the center of the Iraqi capital, and two rounds exploded within the American headquarters area known as the "green zone," (search) the U.S.-led coalition said.

There were no reports of damage or casualties after up to eight detonations thundered through the heart of the capital shortly after 9:30 p.m.

In a statement issued late Tuesday, the Coalition Provisional Authority (search) said two projectiles exploded in the green zone but caused no casualties. The statement said there was no damage to the coalition headquarters, located in the Republican Palace.

After one of the detonations, white smoke could be seen rising from an area just north of the palace.

Iraqi guards working for Iyad Allawi, a member of the Iraqi Governing Council (search), said they counted at least six detonations near the area, along the west bank of the Tigris River.

Iraqi police began setting up checkpoints in the center of the city in an effort to apprehend those responsible.