Military helicopters fly over the entrance to Pakistan's army headquarters after an attack by armed men in Rawalpindi, located on the outskirts of Islamabad, October 10, 2009. [Agencies]

ISLAMABAD: Pakistani aircraft attacked Taliban militants in their South Waziristan stronghold near the Afghan border as the government said a ground offensive against the al Qaeda-linked fighters was imminent.

The aircraft struck the militants late on Sunday, hours after commandos stormed an office building and rescued about 40 people taken hostage after an attack on the army headquarters.

Pakistani Taliban militants linked to al Qaeda have launched numerous attacks on government and foreign targets over the past couple of years killing hundreds of people.

The military has been conducting air and artillery strikes in south Waziristan for months, while moving troops, blockading the region and trying to split off militant factions.

But a ground offensive, in what could be the army's toughest test since militants turned on the state, has yet to begin.

Interior Minister Rehman Malik told Reuters in an interview in Singapore the offensive was "imminent".

"There is no mercy for them because our determination and resolve is to flush them out," Malik said. "They have no room in Pakistan, I promise you."

Malik said members of the Pakistani Taliban and al Qaeda were suspected to have been behind Saturday's attack on army headquarters in Rawalpindi, near Islamabad, which ended a week when suicide bombers struck in the capital Islamabad and Peshawar, killing more than 50 people.

Malik said the offensive against the militants in South Waziristan was no longer a matter of choice.

"It is not an issue of commitment, it is becoming a compulsion because there was an appeal from the local tribes that we should do the operation," he said.

About 28,000 troops have been put in place to take on an estimated 10,000 hard-core Taliban, army officials said earlier.