A gas explosion injured one person and damaged a two-story building in northwestern Pakistan near the Afghan border Saturday. Police initially said it was a bomb but later determined it was an accident.

The conflicting statements reflect the atmosphere of fear that has taken hold in Peshawar, the largest city in the northwest and the main gateway to the Al Qaeda and Taliban-infested frontier region. The area has been increasingly targeted as militants retaliate against an army offensive aimed at routing Taliban militants from a nearby region.

Peshawar has been hit by eight militant attacks in less than two weeks, including a suicide bombing that killed 19 people on Thursday, as militants retaliate against an army offensive that began in mid-October against the Taliban in South Waziristan. Many militants are believed to have fled north to escape the fighting.

Senior officers, including the city's police chief, first said the explosion, which partially destroyed the two-story building, was caused by a bomb.

But Haroon Babar, a senior police officer, said a bomb disposal squad sent to the site found no explosives.

"It seems that a gas pipeline under the wall might have exploded causing the damage," he said.

Pakistan helped nurture a generation of Islamic militants after the Soviet Union invaded Afghanistan in 1979. Following the Soviet withdrawal a decade later, Pakistan helped the Taliban seize control. Many of these militants fled to Pakistan after the U.S.-led invasion of Afghanistan in late 2001.