Four U.S. troops killed in southern Afghanistan

KABUL (Reuters) - Four U.S. service members have been killed in a bomb attack in southern Afghanistan, the latest in a rising tide of violence in the country, international forces said on Friday.

Taliban insurgents have escalated their war against NATO-led troops in recent months and violence has already reached its worst levels since the start of the eight-year-old war.

The NATO-led International Security Assistance Force said in a statement two U.S. service members were killed on the spot in a bomb attack in southern Afghanistan on Thursday, and two more died of wounds later.

General Stanley McChrystal, who now commands more than 100,000 troops in Afghanistan, two thirds of them American, has requested tens of thousands more to fight the Taliban, warning that without them, the war will probably be lost.

In a recent trend, attacks by Taliban fighters have spread from traditional strongholds in the south and east to once-peaceful western and northern parts of the country.