Gunmen shot and killed a Pakistani army brigadier and his driver in the capital, Islamabad, on Thursday as the military continued an offensive against Taliban targets, police said.

It was not clear who was responsible for the attack but it came as the country was on high alert amid fears of retaliatory strikes by militants as the army attacks their stronghold in South Waziristan on the Afghan border.

Gunmen on a motorcycle killed Brigadier Moin Haider and his driver, city police official Tahir Alam said. A guard was wounded.

'Witnesses have told us two men came on a motorcycle and opened fire,' said another city police official Abdul Qadir.   

Military spokesmen were not available for comment.   

Pakistani forces launched an offensive on Saturday to take control of the lawless South Waziristan region after militants rocked the country with a string of bomb and suicide attacks, killing more than 150 people.   

On Tuesday, two suicide bombers attacked an Islamabad university killing at least four people, and the next day authorities ordered schools and colleges to close across the country. Most were closed on Thursday.   

The closure of schools rattled stock market investors and the main index ended 3.36 percent lower at 9,247.78 on Wednesday. The index was up 0.38 percent up at 9,282.68 at 0415 GMT on Thursday.   

Remote and rugged South Waziristan, with its rocky mountains and patchy forests cut through by dry creeks and ravines, is a global hub for militants.

Pakistan's media and public generally back the offensive but the alarm spread by the order to close schools, and the slide in stocks that that triggered on Wednesday, showed public alarm.

An intensification of militant attacks in urban centres could begin to test the public's patience. The Waziristan offensive is expected to take weeks, analysts say. - Reuters