ISLAMABAD, Pakistan — Pakistan banned the Taliban today after they claimed responsibility for one of the country’s worst-ever terrorist attacks, toughening its stance a week after U.S. ally Pervez Musharraf was ousted from power.

The Interior Ministry announced the decision 24 hours after rejecting a Taliban cease-fire offer at Bajur, a rumored hiding place for Osama bin Laden, where an army offensive has reportedly killed hundreds in recent weeks. Another 200,000 people have fled their homes.

“This organization is a terrorist organization and created mayhem against public life,” the ministry chief, Rehman Malik, said in announcing the ban on Tehrik-e-Taliban Pakistan, an umbrella group for militants along the Afghan border created in December to strengthen their fight against the government.

Anyone aiding a proscribed organization — through financial assistance, promoting them in literature, or in other ways — can be jailed for up to 10 years under Pakistan’s anti-terrorism laws.

A spokesman, Lou Fintor, said the U.S. Embassy had seen media reports about the ban. “Pakistan’s leadership has clearly stated their commitment to pursuing and eliminating terrorism and securing Pakistan’s borders for the benefit of its own citizens,” he said.

However, a spokesman for Tehrik-e-Taliban claimed the ban was “meaningless.” “Our organization is neither registered nor do we have any bank accounts,” Muslim Khan said.

The announcement came amid fears among America and other Western nations that the resignation of Mr. Musharraf, a key ally in the war on terror, would affect the nuclear-armed nation’s ability to battle extremist groups, especially with the ruling coalition government teetering on the verge of collapse.

The largest political party, headed by the widow of slain prime minister Benazir Bhutto, was building alliances with smaller parties in Parliament in case it was forced to form a new government, as appeared increasingly likely.

It also was toughening its stance against militants, rejecting a Taliban cease-fire offer on yesterday and then banning the group today.

Mr. Malik said such steps had not been taken earlier because the provincial government had been trying to negotiate with the Taliban.

He said that despite a peace deal struck with some insurgents in Swat, a former tourist destination now beset by fighting, al-Qaida and Taliban-linked militants kept attacking security forces, burning schools and damaging public buildings.

Days after Mr. Musharraf was forced to resign after nine divisive years in power, the Taliban claimed responsibility for a spectacular attack on one of Pakistan’s largest and most sensitive weapons installations.

At least 67 people were killed and more than 100 others wounded in the twin suicide bombings outside a weapons factory near the capital, Islamabad, most of them civilians, in what the Taliban said was revenge for military offensives in Swat and Bajur.

They have claimed responsibility for several strikes since then, including a rocket-and-bomb attack before dawn today on the home of provincial lawmaker Waqar Ahmed Khan in Swat, which killed his brother, two nephews and five guards, police, and the politician said.

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Associated Press Writer Riaz Khan and Nahal Toosi contributed to this report from Islamabad.