ISLAMABAD - Pakistani soldiers secured a fort captured from militants in the northwest of the country on Thursday and consolidated their positions on peaks around another insurgent base, the military said.

The army launched an offensive on October 17 aimed at rooting out and defeating Pakistani Taliban militants in South Waziristan, a lawless ethnic Pashtun region on the Afghan border.

Separately, a U.S. drone aircraft fired two missiles into North Waziristan, another major al Qaeda and Taliban sanctuary in northwest Pakistan, killing four militants, Pakistani intelligence officials said.

The offensive is closely watched by the United States and other powers embroiled in neighboring Afghanistan, as South Waziristan's rugged landscape of barren mountains and hidden ravines has become a global center of Islamist militancy.

Foreign al Qaeda fighters are believed hiding there along with thousands of Pakistani insurgents. Fighting has intensified in recent days as troops advanced from three directions on three main militant bases -- Sararogha, Makeen and Ladha.

The military said on Thursday afternoon 28 militants had been killed in South Waziristan in the previous 24 hours, taking their death toll to 422 since the offensive began. Five soldiers including an officer were killed and two were wounded, the military said.

There has been no independent verification of the casualties as reporters are not allowed into the area except on an occasional trip chaperoned by the military.

Security forces secured the Ladha Fort and consolidated their positions on the peaks in the Sararogha area where the five soldiers were killed in a blast, the military said.

Sixteen militants were killed and five captured in the same area.

The militants are being squeezed out of their strongholds but have retaliated by stepping up bomb attacks on urban targets.

STOCK INVESTORS WORRY

The violence has unsettled trade on Pakistan's stock market and the main index ended 0.47 percent lower at 9,112.10 as investors concerned about security booked profits at higher levels after a 2.4 percent gain the previous day, dealers said.

In North Waziristan, a U.S. drone fired missile at a house in a village about 18 km (12 miles) east of the region's main town of Miranshah, killing four militants, Pakistani officials said.

The United States, facing surging violence in Afghanistan, stepped up its use of the pilotless aircraft to attack targets in Pakistan last year.

The United States has launched 44 such strikes on suspected militants in Pakistan this year compared with 32 last year.

Pakistan officially objects to the strikes, saying they are a violation of its sovereignty and cause civilian casualties which bolster Islamist support, but the missiles have killed some top militants.

Pakistani Taliban chief Baitullah Mehsud was killed in a drone attack in South Waziristan in August.

Pakistan says it has been getting no U.S. help in the South Waziristan offensive and officials have criticized U.S. forces in Afghanistan for abandoning checkpoints over the border, which they said opened up escape routes for fleeing insurgents.

Pakistan Afghanistan