Eight U.S. troops were killed by a roadside bomb in southern Afghanistan on Thursday in the deadliest single attack on foreign forces in a month, the U.S. military said, reported Reuters.

Violence in Afghan has shot up in recent weeks as Taliban-led insurgents ramped up their long- expected spring offensive.

U.S. commanders had warned that a surge in violence was likely, with militants hitting back after NATO-led forces claimed parts of the insurgency's southern stronghold over the last year.

Thursday's bomb was the worst individual attack on foreign troops since eight U.S. service personnel and a U.S. contractor were shot dead by an Afghan air force pilot at a military airport in Kabul on April 27.

The Pentagon and NATO-led International Security Assistance Force (ISAF) in Afghanistan initially said seven troops were killed on Thursday, but later added that an eighth died, the report stated.

In another incident, an ISAF service member was killed earlier when a helicopter crashed in eastern Afghanistan, the coalition said on Thursday. The cause of the crash is under investigation.

The nearly decade-old war in Afghanistan is increasingly unpopular in the United States. Of the roughly 2,480 foreign troops killed in Afghanistan since 2001, more than 1,580 have been U.S. nationals.

The deaths of the troops are on a rise and this has come at a time when lawmakers in U.S Congress narrowly lost a vote that would have required President Barack Obama to promptly withdraw the troops from Afghanistan.

Foreign troops are preparing to start a gradual reduction in forces from July, handing over lead security responsibility to Afghan forces by the end of 2014.

But critics of Obama's war strategy in Congress are calling for a faster drawdown as the number of  civilian and military casualties has reached record levels in 2010, the worst year of the war since U.S.- backed Afghan forces toppled the Taliban in 2001.

A total of 711 foreign troops were killed last year and 2011 is expected to follow a similar pattern, with casualty tolls rising during the spring and summer. Almost 200 foreign troops have been killed in Afghanistan so far in 2011, the report stated.