BAGHDAD — Rockets or mortars hit the American-protected Green Zone early yesterday, just a day after a powerful Shiite cleric, Muqtada al-Sadr, ordered his Mahdi Army militia to extend its cease-fire by another six months.

Nearly 10 blasts could be heard in the sprawling area along the Tigris River that houses the American and British embassies, the Iraqi government headquarters and thousands of American troops. It was not immediately clear whether there were casualties.

An American military spokesman, Major Brad Leighton, confirmed the Green Zone was hit by indirect fire — the military’s term for a rocket or mortar attack — but could not provide more details.

It was the fourth time this week that American outposts in Baghdad appeared to be the targets of rocket or mortar attacks. At least six people have been killed.

The flurry of attacks followed a substantial lull in such violence as security has increased in the capital over the last half-year.

Earlier in the week, the American military blamed Iranian-backed Shiite militias that have broken away from Mr. al-Sadr’s block for the rocket attacks. Iran denies that it sponsors extremists in Iraq.

As the American praised Mr. al-Sadr for extending his cease-fire, it also pledged to pursue the breakaway militias.

“Those who dishonor the Sadr pledge are regrettably tarnishing both the name and the honor of the movement,” it said.

The al-Sadr cease-fire was extended until the 15th of Shaban, a reference to the Islamic month before Ramadan, which would mean mid-August.