Islamabad ? A suicide bomber on a bicycle attacked a major Pakistani air base on Friday, killing seven people in an escalating campaign that strikes at the heart of this nuclear-armed nation’s security forces.

The strike was one of three bombings in northwest Pakistan that killed 24 people and wounded at least 28 as the army pushed a seven-day offensive deeper into al-Qaida and Taliban territory close to the Afghan border.

About 200 people have been killed this month in a string of militant attacks on military, police and civilian targets nationwide. The onslaught is undermining confidence in the U.S-backed government and risks sapping public support for the assault in South Waziristan.

The civilian government and politically powerful military are under intense international pressure to root out Islamist militants that are also blamed for rising attacks on U.S. and NATO troops across the frontier in Afghanistan.

The army has undertaken several offensives along the border in recent years, losing hundreds of soldiers, but questions remain over the country’s commitment to the fight against militants that it nurtured for years for use as proxies in India and Afghanistan.

The bomber blew himself up at a checkpoint on a road leading to the Pakistan Aeronautical Complex at Kamra, about 30 miles from the capital, Islamabad.

Hours later, an explosion struck a bus traveling in the Mohmand tribal region, farther north than South Waziristan.

Four women and three children were among the 17 killed, said Zabit Khan, a local government official. He said it was unclear whether the bus struck a buried bomb or the explosive device was detonated by remote control.

Also Friday, a car bomb exploded in the parking lot of a recreational facility housing a restaurant and a marriage hall in Peshawar, the main city in the northwest. Fifteen people were wounded in that blast.