Four NATO soldiers were killed Monday in a bomb attack in southern Afghanistan, one of the toughest battlegrounds in a nearly 10-year Taliban insurgency, the alliance said in a statement.

The US-led International Security Assistance Force (ISAF), NATO's mission in the war-torn country, did not provide the nationalities of the casualties, leaving it to their native countries to do so.

"Four International Security Assistance Force service members died following an improvised explosive device attack in southern Afghanistan today," the force said without giving any further details.

The latest deaths take to 176 the number of foreign soldiers killed so far in 2011, according to an AFP tally based on data compiled by independent website www.icasualties.org.

Last year, the deadliest so far on record, 711 international soldiers died.

About 130,000 ISAF troops are battling a fierce Taliban insurgency, with most forces in southern Afghanistan from the US or Britain.

The Taliban last month announced the start of a new offensive, vowing to increase bomb attacks and guerrilla-style raids on Afghan troops and their foreign allies.

More than half of ISAF's fatalities are caused by rebel attacks using home-made mines known as improvised explosive devices (IEDs).

The Taliban regime was toppled in 2001 in a US-led invasion for sheltering Osama bin Laden, who was killed in a US raid in the Pakistani garrison town of Abbottabad on May 2.