ISLAMABAD, PAKISTAN - Taliban gunmen who took 42 people hostage at Pakistan's army headquarters were demanding the release of about 100 militants, an army spokesman said Monday, as the death toll from the siege rose to 23.

Giving the first detailed account of the audacious weekend raid, military spokesman Major General Athar Abbas said that 10 militants on Saturday drove up to the army command centre in the garrison city Rawalpindi, near Islamabad.

After a gun battle with security forces at a checkpost which killed five militants and six soldiers, the surviving rebels grabbed 42 mostly military personnel and barricaded themselves in a building, armed with bombs.

"Their target was to take hostage senior officers of the GHQ (General Headquarters) and make demands," Abbas told a press conference.

"They had a long list of terrorists who had been apprehended. The main demand was the release of terrorists including high-profile ones. It included over 100 names, from all the groups, all the terrorists across the board."

The tense siege lasted through the night, before commandos stormed the building on Sunday morning, with three hostages and four militants killed.

Two soldiers died in the raid, with three more succumbing to their injuries Monday.

Security forces arrested the alleged mastermind of the operation - named as Aqeel, also known as Doctor Usman - but he is seriously injured, Abbas said.

The Pakistani Taliban earlier Monday claimed responsibility for the raid.

"We claim responsibility for the attack on GHQ. It was carried out by our Punjab branch... We have the capability to strike at any place in Pakistan," Taliban spokesman Azam Tariq told an AFP reporter by phone.

"As long as Pakistan continues its operation against the Taliban, we will also keep continuing such attacks."

Abbas said the militants had planned the army headquarters raid in the lawless northwest region of South Waziristan bordering Afghanistan, stronghold of the Tehreek-e-Taliban Pakistan (TTP) umbrella movement.

"The main training area for this operation was in South Waziristan," Abbas told reporters.

Military and government officials have said they are planning to launch an all-out military offensive against the TTP in Waziristan, but Abbas would not be drawn on the timing of such an operation.

"The government has taken a principled decision that this organisation is responsible for more than 80 percent of all the suicide attacks, acts of terrorism in this country," he said.

"They have taken a principled decision that there will be an operation in this area. It is now a matter of military judgement, what is the appropriate timing (and) in the best national interests."

Analysts have said a spike in militant strikes - including a suicide blast in the northwest which killed 41 people on Monday - are a tactic by militants to deter such an assault into their sanctuaries. --AFP