KABUL (AFP) - 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," it said without giving any further details. Meanwhile, a Canadian military helicopter slammed into the sands of Afghanistan overnight, injuring four soldiers, a defence official said Monday. The Chinook transport helicopter hit the ground in the dark of night in a remote area of the Panjwaii district, and flipped onto its side, tossing around 25 soldiers and a journalist inside. "The cause of the incident was not due to enemy activity," Captain Jennifer Stadnyk said in a email to AFP, adding an investigation into the cause was underway. Canadian media said the pilot may have misjudged the distance to the ground during a routine landing. Stadnyk said four Canadian soldiers sustained "non-life threatening injuries" in the crash and were being treated for their injuries. The helicopter, which in images broadcast by CBC appeared to be heavily damaged, had been secured and would be transported to a NATO base at Kandahar Airfield.