DERA ISMAIL KHAN: Pakistani jets bombed militant targets in the main insurgent stronghold along the Afghan border Tuesday ahead of an expected ground offensive there, while the army killed 26 insurgents elsewhere in the northwest, authorities said.

The army says 80 percent of the militant attacks plaguing nuclear-armed Pakistan are planned from South Waziristan, while the United States says insurgent leaders blamed for spiraling violence inAfghanistan are also based in the lawless, remote area.

The army and the government have agreed to launch what is expected to a bloody and difficult ground operation in the mountainous region. An army spokesman Monday declined to say when the operation would begin, but there has been speculation it could be imminent.

For the past three months, jets have been bombing target in the region, and the military has been attempting to cut off militant supply and communication lines. Authorities are also trying to secure the support of militant factions that in the past have agreed not to attack Pakistani troops.

Bombing runs Tuesday destroyed around 15 houses in the Makeen, Ladha and Barwand regions of South Waziristan, a local intelligence official said on condition of anonymity because he was not authorized to brief to the media.

In a reminder of the reach of the militants, authorities said helicopter gunship attacks killed 26 insurgents in Bajur, a tribally administered region that is 185 miles (300 kilometers) north of Waziristan. The army undertook a major offensive there six months ago and declared it free of insurgents, but some still remain.

Abdul Malik, a local government official, said the attacks took place in Damadola and Sawai, known as militant-held areas. He said he got the information about militant casualties from intelligence and military sources.

The militant threat to Pakistan has been highlighted by four major terrorist attacks over the last nine days, including a suicide attack on a U.N. office in the capital that killed five staffers and a 22-hour siege on the army's headquarters over the weekend.