Mortar rounds slammed into the US-controlled Green Zone on Tuesday and a central Baghdad street being reopened to the public, officials said. At least four people were injured, all of them on the central street, officials said. The attack occurred just before 4 p.m., with at least two rounds exploding in the Green Zone and two others across the Tigris River on Abu Nawas Street, police said. The Iraqi government has recently announced plans to reopen the street, known for its fish markets and riverside restaurants, before the US-led invasion of March 2003. The US Embassy confirmed explosions in the Green Zone but said no casualties were immediately reported. "Preliminary information indicates that there were no casualties and minimal damage," embassy spokesman Lou Fintor said. A recent increase in mortar and rocket attacks on the Green Zone, which houses the US Embassy and major Iraqi government offices, has raised concern, especially since they are occurring during the US-led crackdown. The US 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 US 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.