Four US troops were killed in Afghanistan when Taliban militants shot down a NATO helicopter.

The International Security Assistance Force (ISAF) helicopter was brought down on Wednesday in Helmand province in southern Afghanistan by hostile fire, a military spokesman announced late on Wednesday.

The latest incident brings the death toll for troops of the US-led coalition to 23 this week, he added.

He confirmed the four soldiers killed were US servicemen.

Taliban spokesman Yousuf Ahmadi telephoned AFP from an undisclosed location to claim responsibility, saying, “We brought it down with a rocket. It crashed in the Sangin district bazaar.”

Earlier in the day, the US-led coalition had announced that one of their soldiers had been killed by a bomb explosion in southern Afghanistan.

On Tuesday, CNN announced that according to its statistics, 1,001 US troops have been killed in the 104 months of combat in Afghanistan.

From 2001 through 2006, the casualty rate for US troops never reached 100 in any single year.

But that number started going up in 2007 and spiked to more than 300 last year. If the current rate continues, 2010 will be the deadliest year of the war for the US-led troops.