Baghdad, Iraq — A barrage of rockets hit Baghdad's fortified Green Zone Saturday, casting doubt on the influence of a Shiite militia cease-fire fewer than 24 hours after it was renewed.

At least six blasts resonated across the U.S.-protected enclave, which is home to Iraqi government offices, the U.S. Embassy and military bases. An American official said there were no casualties and no significant damage.

Along Iraq's frigid northern border, Turkish forces pressed their largest ground offensive against Kurdish separatist guerrillas in years, pounding rebel targets with artillery and helicopter gunfire.

The Turkish military command claimed that as many as 79 rebels had been killed along with seven of its troops since the incursion began Thursday night.

Ahmed Denis, a rebel spokesman, declined to confirm the number of Kurdish casualties, but said they had recovered the bodies of 15 Turkish soldiers. He also claimed they shot down a Turkish helicopter Saturday.

Neither side's account could be verified.

The Green Zone attack was the fourth rocket barrage this week in the capital, where U.S. commanders have touted a more than 60 percent decline in violence since June.

Navy Rear Adm. Gregory Smith, a military spokesman, blamed the previous attacks on breakaway factions of radical Shiite cleric Muqtada al-Sadr's powerful Mahdi militia, groups that U.S. commanders allege receive support and direction from Iran. There was no immediate comment on who might have been behind the new Green Zone attack but previous attacks on the fortified area have been blamed on Shiite militias.

The attacks took place despite a six-month truce declared by al-Sadr in August and renewed Friday in a much-anticipated announcement read-out in mosques during midday prayers.They raised questions about the anti-American cleric's ability to rein in the splinter groups, which have ignored his order to stand down.

Many in al-Sadr's movement are disgruntled with the truce, which they claim has been used by the U.S. military and Shiite rivals within the Iraqi security forces to target his followers.

Mahdi militiamen helped drive the sectarian killing that once left dozens of bodies in the streets every day; three bodies were found on Saturday.

U.S. officials say al-Sadr's cease-fire played a key part in the ebb in violence since the American forces completed a buildup of 28,500 additional troops, most of whom are due to leave this year. They also credit a rebellion by tens of thousands of Sunni Arab tribesmen against the Islamic extremists they once backed.

On the Turkish front, Prime Minister Nouri al-Maliki received a telephone call from his Turkish counterpart, Recep Tayyip Erdogan. The Iraqi leader warned Erdogan to avoid actions that could threaten stability in the semi-autonomous Kurdish region or hurt civilians, al-Maliki's spokesman Ali Dubbagh told reporters Saturday.

Turkish officials have said they are targeting only hide-outs of the Kurdish Workers Party, or PKK, which uses the border region to launch attacks on their forces.

There have been conflicting accounts of the scale of the offensive. Turkish media reports say about 10,000 troops have pushed more than 10 miles into Iraq in pursuit of the militants, but Iraqi and rebel officials say the invading force is much smaller.

Kurdish authorities on Saturday pulled back members of the regional Peshmerga security force to avoid a clash with the Turkish troops, but vowed to respond forcefully to any attacks on Kurdish civilians.

The United States, which has confirmed that it received advance notice of the Turkish operation, has urged restraint. The U.S. considers the PKK a terrorist organization and has said that Turkey has the right to defend itself.

In other developments Saturday, at least four people drowned when a boat carrying Shiite pilgrims to Karbala for a religious festival capsized in the Tigris River north of Kut, police said. Rescue efforts continued for two others missing in the accident.

More than 4 million pilgrims so far have converged on Karbala for next week's Arbaeen rites, which mark the 40th day of mourning following the anniversary of the death of Imam Hussein, one of Shiite Islam's most revered figures.

In Baghdad, Shihab Timimi, the head of Iraq's main journalists union, was wounded along with his son when gunmen opened fire on their car, colleagues said.

Special correspondent Asso Ahmed in Sulaymaniya, Yesim Comert in Istanbul and Saad Fakhrildeen in Najaf contributed to this report, along with correspondents in Baghdad.

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