Violence continues in Iraq, where explosions and attacks have killed at least 30 people and wounded dozens of others.

In Baghdad's Sadr City suburb, witnesses say at least one rocket slammed into a busy market Saturday, killing at least 13 and wounding about 30 others.

Another Iraqi was killed in a separate attack in Sadr city.

North of Baghdad, five U.S. soldiers were killed early today when two rockets slammed into their base in Taji. Six other soldiers were wounded, some critically. U.S. military spokesmen say the truck used to fire the rockets was destroyed by a military helicopter.

South of Baghdad, local reports say two other U.S. soldiers were killed in an attack in Kut, but the U.S.-led coalition has not yet confirmed that incident.

In Karbala, Polish troops clashed overnight with insurgents, killing five.

And in Tikrit, Saddam Hussein's home town, an apparent suicide car bomb attack killed at least four people. Some of the victims were Iraqi police, but U.S. spokesmen say no Americans were injured in that attack.

Meanwhile, the top U.S. military commander in the Middle East is quoted Saturday as saying he might ask for more troops because of the deteriorating security situation.

General John Abizaid told the The New York Times that the next four months will be critical with further insurgent attacks against American troops likely. He also expressed doubts about the current reliability of Iraqi security forces.

His comments come as Iraq approaches June 30 -- the deadline the United States has set for a handover of sovereignty to an interim Iraqi government.

The United States now has 135,000 troops in Iraq.

In other developments Friday, the radical Iraqi Shi'ite Muslim leader Moqtada al-Sadr threatened to unleash suicide bombers against coalition forces if they attack his stronghold in the city of Najaf.