Iraqi authorities on Friday lifted a curfew imposed on Shiite Islam's holiest city of Najaf in a bid to thwart attacks a day after 73 people died in twin suicide bombings in nearby Hilla.
In Baghdad, the US military was investigating reports that another helicopter had gone down near Taji, north of the Iraqi capital.
If confirmed, it would be the third US military helicopter lost in two weeks. A private US security chopper also crashed in Baghdad on January 22.
In the central city of Najaf, a curfew which was imposed late Thursday was lifted after dark on Friday.
"The curfew has been completely lifted from Najaf and the surrounding towns including Kufa," Najaf police spokesman Ali Jariu said.
Najaf provincial spokesman Ahmad Duaibel said the curfew was imposed after the authorities received information that armed groups planned to launch attacks against the city.
On Sunday, Iraqi and US forces fought members of a Shiite sect north of Najaf, killing more than 250 "Soldiers of Heaven," wounding more than 200 and arresting almost 300.
Officials said the well-armed militia and its cult leader planned to attack senior Shiite clerics in Najaf and occupy holy sites there.
On Friday, security around offices and residences of Shiite clerics such as Grand Ayatollah Ali al-Sistani and the holy shrine of Imam Ali was stepped up, police said.
In Baghdad, US Lieutenant Colonel Josslyn Aberle said the military was checking reports of another helicopter crash after an Iraqi army source reported that soldiers saw one fall to the earth near the sprawling US military base in Taji.
"We don't know the reasons for the crash, nor its exact site because the US army has sealed off the area," the source said.
On January 20, a Black Hawk helicopter crashed northeast of Baghdad, killing 12 troops, and a US attack helicopter went down Sunday north of Najaf during the battle with Shiite militiamen, killing its two-man crew.
At least 73 people were killed in a twin suicide bombing Thursday in the centre of Hilla, the predominantly Shiite capital of Babil province.
The attacks came as Iraqi officials said that nearly 2,000 civilians had been killed in the raging sectarian conflict across the country in January.
On Friday, two more people were reported killed in rebel attacks.
In Washington, a report concluded that US President George W. Bush's plan to send 21,500 troops to Iraq to help stem sectarian bloodshed could result in an increased force of up to 48,000 soldiers, when non-combat support troops were included.
Iran, meanwhile, blamed Washington again for Iraq's ongoing turbulence.
"The United States, despite the presence of hundreds of thousands of troops, is unable to achieve its objectives," said Foreign Minister Manouchehr Mottaki.
"It has failed in Iraq, in Lebanon, in Palestine," he said. "And in the face of its failures, it is hunting for a scapegoat and so accuses Iran."
Washington has repeatedly accused Tehran of arming militias in Iraq and some US officials have suggested Iran was behind a recent attack in the shrine city of Karbala where five US soldiers were killed.
The military reported the deaths of three soldiers in vehicle accidents, taking losses since the March 2003 invasion to 3,083, according to Pentagon figures.
A separate statement said US forces had killed 18 insurgents in the western Sunni bastion town of Ramadi in two battles over the past two days.
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