Relatives of an Afghan family carry the dead bodies of two children killed by a rocket in Kunday village in Khost province, southern Afghanistan on Sunday, June 22, 2008.


KABUL -- Militants in Pakistan fired rockets at NATO bases across the border in Afghanistan, killing three children in a village and prompting the alliance to launch a pair of retaliatory artillery strikes, officials said Sunday.

The clashes could heighten diplomatic tension over Pakistan's inability to stop Islamic militants from operating from its territory -- and whether forces in Afghanistan have the right to strike back.

NATO said five rockets were fired at one of its bases in Khost province overnight. At least one hit a house in Kunday, a small village which sits between two military bases, killing the three children. Another hit a NATO base, injuring an Afghan man.

Relatives of the children carried three caskets, draped in colourful clothes, to a graveyard for burial Sunday morning.

NATO said its forces responded "in self-defence'' to the attack with artillery fire on the launch site inside Pakistani territory.

In an earlier attack Saturday, three rounds of "indirect fire'' -- which often refers to mortar or rocket attacks _ landed near a NATO outpost in neighbouring Paktika province, the alliance said. Three more landed in an Afghan army compound. No casualties were reported.

NATO said those rounds also came from inside Pakistan and responded with artillery fire.

Last year, more than 8,000 people were killed in insurgency-related attacks in Afghanistan _ the most since the 2001 U.S.-led invasion. Violence has claimed more than 1,700 lives so far this year.

Pakistan, like Afghanistan, is a key ally of the United States in its six-year campaign against international terrorism.

But Afghan and U.S. officials blame surging violence in Afghanistan in part on efforts by the new Pakistani government to make peace with Taliban militants on its side of the mountainous frontier blamed for suicide attacks in Pakistan.

Pakistan's army has pulled back some forces from its lawless tribal areas, where al-Qaida and the Taliban find refuge, and has largely held fire during the peace talks -- a pause critics say has allowed insurgents to intensify strikes into Afghanistan.

Relations were further strained when U.S. warplanes apparently bombed a Pakistani border post in the Mohmand tribal region this month, killing 11 Pakistani troops -- one of a series of cross-border strikes which Islamabad has condemned as an infringement of its sovereignty.

U.S. Secretary of State Condoleezza Rice has expressed regret over the Mohmand incident. However, it remains unclear why the Pakistani post was struck.

Asked about the latest NATO artillery strikes, Maj.-Gen. Athar Abbas, spokesman for the Pakistan army, said its troops also fired mortar rounds and small arms at the "miscreants'' who attacked the base in Paktika. He reported no casualties.

He said there was an "understanding'' that Pakistani forces would engage militants on its side of the border, and had no confirmation of NATO's assertion that it immediately informed Pakistani forces it was under attack.

"If they are doing it (returning fire) on their own, it is not correct,'' Abbas said.