Washington, Jan 21 (DPA) At least 19 US soldiers were killed in Iraq in one of the deadliest days since the 2003 US-led invasion, the US military said.

A helicopter crash near Baghdad Saturday killed 13, while five soldiers died in a militia attack on a security centre in Karbala.

Another soldier died in a roadside bomb attack in northern Iraq, while two soldiers, including a marine, were killed Friday in separate attacks in al-Anbar and Ninewah province.

The deaths come as US President George W. Bush is preparing to send over 20,000 additional troops to Iraq in an effort to quell sectarian violence in Baghdad, which has put the country on the brink of civil war.

The helicopter, which often transports civilians in addition to military personnel, crashed in an "explosive" region northeast of Baghdad, which is inhabited by Sunnis, Shias and Kurds, news broadcaster CNN reported.

However, US soldiers were able to secure the crash site and seal it off. The circumstances of the helicopter crash were not yet known and an investigation is underway, a spokesperson said.

In Karbala, an "illegally armed militia group" attacked the Provincial Joint Coordination Centre, where US and Iraqi forces hold security meetings, killing five US soldiers.

"At the time of the attack, US and Iraqi soldiers were meeting to develop a security plan for Shias attending Ashura commemorations," said Brigadier General Vincent K. Brooks, deputy commander of coalition forces in Baghdad.

"The attack ... was aimed at coalition and Iraqi security forces working together towards a better future for the citizens of Karbala," Lieutenant Colonel Scott R. Bleichwehl, spokesperson for coalition forces in Baghdad, said in a statement.