Pakistan clears way for ex-official

The ruling is likely to ease political tensions in the short term but could ultimately pose a challenge for President Asif Ali Zardari, who is Sharif's main rival and whose own popularity has plummeted. Although elections are not due until 2013, Sharif is now in position to reclaim the office he held twice in the 1990s.

"This is a decision welcomed by the entire nation," Sharif told reporters in the eastern city of Lahore, his base. "Today an independent judiciary is giving independent decisions."

Sharif and his brother Shahbaz had been banned from electoral politics because of previous criminal convictions that they say were politically motivated.

The brothers' reinstatement had been widely expected. Earlier this year, Nawaz Sharif led a successful movement to restore the chief justice of the supreme court, whom then-president Pervez Musharraf fired in late 2007.

In a statement yesterday, Zardari congratulated Sharif and welcomed him back to electoral politics. But Sharif's branch of the Pakistan Muslim League represents the main opposition to Zardari's Pakistan People's Party, and the enmity between the men is well known.

For now, though, Sharif is supporting Zardari on several issues, most crucially the military's operation in the Swat Valley, which continued yesterday.

Since early May, the army has been battling to oust Taliban militants who had taken control of the northwestern region. About 2.3 million people have fled since fighting began, according to provincial government statistics, but about 200,000 civilians remain trapped.

Human Rights Watch warned yesterday that unless the government relaxes a curfew and allows food, water, and medicine into the valley, there will be a "humanitarian catastrophe."

But Major General Athar Abbas, a military spokesman, said it would not be possible to pause the offensive. "Lifting the curfew would mean letting the operational situation slip out of hand," he said. The government said that instead it was planning an air drop of supplies to trapped residents.

Abbas insisted that the government has the Taliban fighters on the defensive, although that was impossible to verify because access to Swat is severely limited. "They're in disarray and finding ways to sneak out," he said.

Meanwhile, the army attacked Taliban positions in another of the group's northwestern strongholds, the tribal region of South Waziristan, which is home to top Taliban leader Baitullah Mehsud. Several militants were killed, according to residents, and the attack fueled speculation that the army is preparing to enter that area. Zardari said recently that South Waziristan would be next on the army's agenda after Swat.

The military launched the operation in Swat after the Taliban moved into the adjacent districts of Buner and Dir, in violation of a peace deal with the government. The United States has leaned heavily on the Pakistani government to take a tougher line in combating militancy.