Pakistani air strikes killed at least 21 militants Sunday in attacks on their hideouts in a restive northwestern tribal areas bordering Afghanistan, officials said.

The attacks were launched in the Kuki Khel area of the Khyber tribal district, where the Taliban and another banned Islamist group, Lashkar-e-Islam, have taken refuge.

"In precision air strikes, at least 10 militants were killed and their three hideouts were destroyed in Khyber," a senior military official told AFP on condition of anonymity.

Separate airstrikes also killed eleven other militants in the remote Datta Khel village of restive North Waziristan tribal district and destroyed two militant hide outs, the official said.

Local government and intelligence officials confirmed the death toll.

Pakistan has been battling Islamist groups in its semi-autonomous tribal belt since 2004 after its army entered the region to search for Al-Qaeda fighters who had fled across the border following the US-led invasion of Afghanistan.

In June the army began an offensive in the North Waziristan district after a bloody raid on Karachi Airport ended faltering peace talks with the Taliban.

North Waziristan had become a major base for the Tehreek-e-Taliban Pakistan, which rose up against the state in 2007.

The United States had long called for military action in the tribal areas because militant groups there had targeted NATO forces in Afghanistan.

Pakistan's army says it has killed more than a thousand militants and lost 86 soldiers since the start of the operation.

The death toll and identity of those killed is impossible to verify because journalists do not have regular access to the conflict zones. Critics say many of the dead were non-combatants.