BAGHDAD, Jan 21: The US military on Sunday announced that 3,200 troops had arrived in Baghdad as part of the new security plan as 25 American soldiers were killed across Iraq on Saturday in one of the deadliest days for the US forces since the Iraq invasion.

A brigade of the US 82nd Airborne Division, part of the 21,500 troop build-up ordered by US President George W. Bush, had arrived in Baghdad and would be ready to join the fresh drive to quell sectarian violence in the capital, the American military said in a statement.

The US paratroopers in Baghdad make up the first of five US brigades due to deploy alongside nine Iraqi brigades in the capital.

The brigade will "assist Iraqi Security Forces to clear, control and retain key areas of the capital city in order to reduce violence and to set the conditions for a transition to full Iraqi control of security in the city," the statement said.

“The effort represents the first of several planned troop movements that will assist Iraqi security forces in reducing violence and protecting Iraqi citizens,” the statement said.

The new security plan aims to crack down mainly on Baghdad militias which are involved in killing people from the rival Shia and Sunni communities.

According to the US military, 25 troops were killed on Saturday alone, making it one of the bloodiest days for the American forces since January 26, 2005, when 36 servicemen died.

The military, in a series of statements piling up the body count, listed a helicopter crash, insurgent attacks and roadside bombs as being responsible for Saturday's high casualty rate.

Five troops, it said in a statement on Sunday, died in separate `enemy’ attacks in the western Sunni Al-Anbar province, a hotbed of anti-US insurgency where the military has lost the bulk of its troops since the Iraq invasion began.

In another daring attack by militants, five soldiers were killed in the southern holy city of Karbala during a meeting to plan security measures for the 10-day mourning ceremony of Aashura that began on Sunday.

The attack was carried out by militants wearing uniforms similar to those worn by Iraqi and US soldiers, the governor of Karbala Akhil al-Khazali said.

“The provincial joint coordination centre in Karbala was attacked with grenades, small arms and indirect fire by an illegal armed militia group,” the military said earlier on Sunday.

Aashura, which commemorates the seventh-century martyrdom of the holy Prophet’s grandson Imam Hussein in Karbala, has been marred in recent years by attacks by Sunni extremists that have killed scores of people.

The worst incident for the military was when a Blackhawk transport helicopter went down northeast of Baghdad on Saturday afternoon, killing 12 service members on board.

Three other soldiers were killed in separate attacks across the country.

The latest fatalities took the military's losses in Iraq since the invasion to 3,050.

As the death toll surged, a Newsweek poll found that more than two-thirds of Americans opposed sending 21,500 more troops to Iraq, the cornerstone of Bush's policy shift for the war-torn nation.

About 68 per cent said Washington should not send additional troops, while 26 per cent support the increase.

In what is seen as part of the crackdown, Iraqi and US troops arrested on Friday a senior aide of radical Shia cleric Moqtada al-Sadr, saying he was operating an illegal armed group engaged in killing civilians.

Sheikh Abdul Hadi al-Darraji was seized with four others from a religious site near Baghdad's Shia district of Sadr City — a bastion of Sadr loyalists and his militia, the Mahdi Army.

Meanwhile, the political bloc of Sadr ended on Sunday its two-month boycott of the Iraqi parliament and government. The group which has six ministers in Maliki's cabinet and 32 MPs in the 275-member parliament said their conditions to end the suspension had been met.—Agencies.