Iraqi authorities clamped a total curfew on Shiite Islam's holiest city of Najaf yesterday to thwart attacks a day after 73 people died in twin suicide bombings in nearby Hilla.
In Baghdad, the US military was probing reports that another of its helicopters 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 Jan. 22.
In the central Iraqi city of Najaf, "the curfew imposed overnight has been extended and includes the entire region around Najaf including Kufa, northeast of the holy city," police said.
Najaf provincial spokesman Ahmad Duaibel said: "Authorities took this decision after receiving 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 by the time fighting ended early on Monday, a defense ministry spokesman said.
Officials said earlier this week that the well-armed militia and its cult leader planned to attack senior Shiite clerics in Najaf and occupy holy sites there.
In Baghdad, US Lieutenant Colonel Josslyn Aberle said yesterday that the military was checking reports of another helicopter crash.
"We're looking into reports of a helicopter going down north of Baghdad at this time," she said.
An Iraqi army source reported that soldiers saw the US aircraft 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 Jan. 20, a Black Hawk helicopter crashed northeast of Baghdad, killing 12 troops, and a US attack helicopter went down on Sunday north of Najaf during the battle with Shiite militiamen, killing its two-man crew.
At least 86 people died in Iraq on Thursday as security officials reported that bitter sectarian attacks had claimed the lives of nearly 2,000 civilians throughout the country last month.
Two suicide bombers killed 73 people and wounded 163 on Thursday when they targeted the center of Hilla, the predominantly Shiite capital of Babil province south of Baghdad, security and medical sources said.
The initial blast sent a panicked crowd fleeing in the direction of the second bomber, who then blew himself up, police officer Kazem al-Shamari said.
Also on Thursday in southern Iraq, a mass grave containing the remains of 200 to 250 people -- probably Kurds -- was discovered near the border with Saudi Arabia, a provincial official said.
Amin Mohammed Amin said the grave was found west of the town of Salman, less than 1km from a former detention camp, thanks to reports from inhabitants of the mainly deserted region.
The grave extended over more than 200m2 and included the bodies of men, women and children in Kurdish clothing, he added.
In Washington, a report concluded on Thursday that US President George W. Bush's plan to send 21,500 troops to help stem sectarian bloodshed could result in an increased US force of up to 48,000 soldiers.
The Congressional Budget Office said that when non-combat support troops were included, the real number of additional troops deployed in Iraq could reach 35,000 to 48,000.