At least one mortar or rocket slammed into the U.S.-controlled Green Zone on Tuesday, wounding five American Embassy contractors, a spokesman said.

The explosion occurred at 3:59 p.m. local time, U.S. Embassy spokesman Lou Fintor said, adding the nationalities of the five embassy contractors who were wounded have "not yet been confirmed."

Fintor said there were no deaths and property damage was minimal.

Iraqi police said earlier Tuesday that mortar rounds had struck the Green Zone, also known as the International Zone, and a central Baghdad street being reopened to the public on the other side of the Tigris River.

"At least one round of indirect fire impacted the International Zone. The nature of the indirect fire remains under investigation," Fintor said. Indirect fire can mean a mortar or a rocket attack in military terminology. "The embassy is open and functioning normally."

Fintor said he had no information about explosions outside the Green Zone, which sits on the west side of the river.

Iraqi police said earlier that two mortar rounds also hit Abu Nawas Street, wounding four Iraqi civilians. The Iraqi government has recently announced plans to reopen the street, known for its fish markets and riverside restaurants, before the U.S.-led invasion of March 2003.

A recent increase in mortar and rocket attacks on the Green Zone, which houses the U.S. Embassy and major Iraqi government offices, has raised concern, especially since they are occurring during the U.S.-led crackdown.

The U.S. Embassy has ordered its staff to wear flak jackets and helmets while outdoors or in unprotected buildings. The order was issued one day after a rocket attack killed four Asian contractors in the zone.

The U.S. is planning to open a massive new embassy in the Green Zone this year despite the ongoing security threat there.

It's unclear what groups have been responsible for the recent attacks. Some barrages have been launched from Shiite-dominated areas in eastern Baghdad, but the Green Zone is also within range of Sunni militant strongholds to the south.