Troops sent to repel a Taliban advance toward the Pakistani capital killed 14 suspected militants, the army said Thursday, and accused insurgents of holding an entire town hostage.
In another development, officials said gun attacks in the mega-city of Karachi killed at least 34 people and threatened to ignite ethnic tension.
President Barack Obama said he was "gravely concerned" about the nuclear-armed country's stability, while Pakistan's president urged the public to support the army offensive so that the Islamic nation would remain under "a moderate, modern and democratic state."
Security forces backed by warplanes began pushing into Buner, a district some 60 miles from Islamabad, on Tuesday after Taliban militants from the neighboring Swat Valley infiltrated the area under cover of a peace pact.
On Thursday, troops ousted militants from the Ambela Pass leading over the mountains into Buner and were inching toward the north, army spokesman Maj. Gen. Athar Abbas said.
Soldiers opened fire on four suspected suicide car bombers who drove toward them near the pass, Abbas said. Two vehicles exploded while the other two managed to drive away. No troops were hurt, he said.
Troops also destroyed four militant vehicles in Dir, a district to the west, Abbas said. At least 14 militants were killed, and one soldier was injured in the previous 24 hours, he said.
Abbas also said militants, who have kidnapped dozens of lightly armed police and paramilitary troops, had burned a police station farther north and sealed off the town of Sultanwas.
"The people of Sultanwas are in great distress," Abbas said at a news conference. "Nobody is being allowed to move out of Sultanwas."
A Taliban spokesman could not be reached immediately for comment.
Security forces barred some reporters from entering Buner and telephone connections were cut, making it hard to verify the army's account of the fighting.
U.S. leaders sharply criticized Pakistani President Asif Ali Zardari's decision to sign a law imposing Islamic law in Swat and the surrounding Malakand region in an attempt to halt two years of bloody and inconclusive fighting.
Defenders of the pact say the Islamic law concession will isolate hard-liners bent on destabilizing the country and bolster thin public support for a crackdown. Officials said Thursday the Islamic courts will be up and running within days.
The "time has come for the entire nation to give pause to their political differences and rise to the occasion and give full support to our security forces in this critical hour," Zardari said in a statement late Wednesday.
"This is the only way to demonstrate our will to keep Pakistan as a moderate, modern and democratic state where the rights of all citizens are protected," he said.
Nuclear arsenal secure?
The Obama administration, determined to stop militants from using Pakistan as a base for attacks in Afghanistan, is asking Congress for more money to aid the Pakistani army.
In a news conference Wednesday marking his first 100 days in office, Obama said Pakistan was potentially unable to deliver basic services to its population such as health care and education.
Obama expressed confidence that Pakistan's nuclear arsenal will be secured because he said he believes Pakistan's army will do the job. But he left the door open for U.S. action if necessary.
Pakistan's stability is complicated by deep ethnic and sectarian tensions that are likely to grow as a result of a marked slowdown in economic growth.
Competition for jobs and political power is sharpest in Karachi, a teeming southern port with a history of ethnic violence where Wednesday's shooting broke out.
Much of the tension has been between the Pashtun population, who dominate the violence-plagued northwest, and Urdu-speaking Mohajirs descended from migrants from India.
The main Mohajir political party that runs the city, the Muttahida Quami Movement, has been outspoken against the Pashtun-dominated Taliban and has warned that the militants represent a growing threat in Karachi, Pakistan's 16-million strong commercial hub.
The city was largely crippled Wednesday after two MQM activists were gunned down by unknown shooters, sparking street violence that had abated by dawn.
Paramilitary rangers roamed the city's trouble spots Thursday, as hospital doctors and police said the death toll had reached 34, with about 50 others injured.
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