KABUL, Afghanistan - Insurgents firing rockets, mortars and automatic weapons launched a ground assault Saturday against NATO's biggest base in southern Afghanistan, wounding several coalition troops and civilian employees in the second such attack on a major military installation this week, officials said.

A Canadian Press news agency report from the Kandahar Air Field said artillery and machine gun fire reverberated through the base, about 300 miles southwest of Kabul, several hours after the attack began. Militants unleashed rockets and mortars and then tried unsuccessfully to storm the northern perimeter, officials said.

No one immediately claimed responsibility for the assault - the third major attack on NATO forces in Afghanistan in six days - but the Kandahar area is a Taliban stronghold.

On Tuesday, a Taliban suicide bomber attacked a NATO convoy in the capital, killing 18 people including six NATO service members including five Americans and a Canadian.

The next day, dozens of Taliban militants attacked the main U.S. military base - Bagram Air Field - killing an American contractor in fighting that lasted more than eight hours.

Navy Cmdr. Amanda Peterseim, a spokeswoman for NATO forces at Kandahar, said at least five rockets struck the base in the initial attack, but witnesses said explosions continued through much of the night. There were no reports of deaths and she did not have the precise number of wounded.

NATO said troops and civilians were told to remain in bunkers as a precaution.