Q+A: Pakistan's war against its Taliban foe

ISLAMABAD (Reuters) - Pakistani commandos stormed an office building on Sunday and rescued 39 people taken hostage by suspected Taliban militants took hostage after a brazen attack on the headquarters of the army.

Saturday's militant raid on the tightly guarded army headquarters in Rawalpindi city came as the military prepared a major offensive against the militants in their northwestern stronghold of South Waziristan on the Afghan border.

Here are some questions and answers about the militant attack and its implications.

WHO WAS RESPONSIBLE?

The government says the Pakistani Taliban under the leadership of their new commander, Hakimullah Mehsud, was responsible. Mehsud met a small group of reporters last week and threatened revenge for the August 5 killing in a U.S. missile strike on then Taliban leader, Baitullah Mehsud. At least some of the gunmen were believed to be militants from Punjab province who are close Taliban allies. Many Punjabi militants, who have long been involved in the anti-Indian insurgency in the disputed Kashmir region, are based with the Taliban in South Waziristan. Some of the hostage takers' phone calls were intercepted and they were speaking Punjabi, a security official said. WILL THE ATTACK WEAKEN GOVERNMENT RESOLVE?

On the contrary, the interior minister said on Saturday the attack, the third major militant attack in less than a week, only underscored the need to finish off the militants with an offensive. The strike at the very heart of the military will be a blow to the defenders of the nation and they will be keen to restore their standing with tough action against the militants, analysts say. WHEN MIGHT THE OFFENSIVE BEGIN?

The military says its operation in South Waziristan has already begun. For months, the military has been launching air and artillery strikes, while moving troops, blockading the region and trying to split off factions. The military has declined to say when ground troops will begin their offensive. Snow is likely by late November, but some analysts argue snow will be more of a problem for the militants, who use high mountain trails that will become impassable, than for the military which has some cold-weather warfare capability and aircraft for transport.

WHAT PROSPECTS FOR THE OFFENSIVE?

The fighting is expected to be much tougher than it has been in the Swat valley, northwest of Islamabad, where the army has largely cleared insurgents in an offensive launched in April. The army says two divisions, or up to 28,000 soldiers, are in place, which it says is a sufficient force to take on an estimated 10,000 hardcore Taliban in South Waziristan. The region is criss-crossed by mountain ridges laced by ravines and dried up creeks of which the military has little knowledge. Standard counter-insurgency doctrine suggests a soldier to insurgent ratio of up to 10:1. Some analysts doubt that enough troops are in place, especially if they have to block members of other Taliban factions based in North Waziristan coming to the help of their South Waziristan comrades. Pakistan had earlier cited shortages of helicopters, armored vehicles and precision weapons in putting off the assault. But U.S. defense officials, keen to see Pakistan end militant support for the Afghan insurgency, said last week Pakistan had mobilized enough forces and equipment for the offensive. U.S. officials acknowledge Pakistan needs more armored vehicles and night-vision devises and one said the Pentagon was trying to free up helicopters and other equipment.

(Additional reporting by Zeeshan Haider; Editing by Bill Tarrant)