ISLAMABAD, Pakistan — Police rounded up hundreds of opposition leaders and rights activists Sunday after Pakistan's military ruler suspended the constitution, ousted the top judge and deployed troops to fight what he called rising Islamic extremism.

Increasingly concerned by the unfolding crisis, the Bush administration said Sunday that American aid to Pakistan would be reviewed. The U.S. has provided about $11 billion to Pakistan since 2001, when Pakistan's president, Gen. Pervez Musharraf, allied with the United States after the Sept. 11 attacks.

"Some of the aid that goes to Pakistan is directly related to the counterterrorism mission," Secretary of State Condoleezza Rice told reporters traveling with her. "We just have to review the situation. But I would be very surprised if anyone wants the president to set aside or ignore" the responsibility to national security that can come through such cooperation, she said.

In the lawless Afghan border region, militants freed 211 Pakistani soldiers captured two months ago, the army's top spokesman said.

Musharraf, a 1999 coup leader who had promised to relinquish his army post and become a civilian president this year, declared a state of emergency Saturday night, dashing hopes of a smooth transition to democracy for the nuclear-armed nation.

Musharraf's leadership is threatened by the reemergence of political rival and former Prime Minister Benazir Bhutto, an increasingly defiant Supreme Court set to rule on the validity of his recent presidential election win, and an Islamic militant movement that has spread from border regions to the capital.

South Waziristan, the tribal border region where the government is struggling to assert control, has seen a surge in violence, including the capture of the soldiers two months ago. The group was freed Sunday through the efforts of a jirga or a tribal council of elders in South Waziristan, said Maj. Gen. Waheed Arshad.

Crucial parliamentary elections expected in January could now be delayed by up to a year, Prime Minister Shaukat Aziz said, stressing that such a decision had not yet been reached. He said the extraordinary measures would be in place as long as necessary.

Aziz said up to 500 opposition activists had been arrested nationwide in the last 24 hours, about 45 of them in the capital, Islamabad.

Among them were Javed Hashmi, the acting president of the party of former Prime Minister Nawaz Sharif; cricket star-turned politician, Imran Khan; Asma Jehangir, chairman of the independent Human Rights Commission of Pakistan; and Hamid Gul, former chief of the main intelligence agency and a staunch critic of Musharraf's support for the U.S.

Some 200 armed police stormed the rights commission office in Lahore on Sunday and arrested about 50 activists, said Mehboob Ahmed Khan, a legal officer for the body.

"They dragged us out, including the women," he said from the police station in the eastern city. "It's inhuman, undemocratic and a violation of human rights to enter a room and arrest people gathering peacefully there."

Attorney General Malik Mohammed Qayyum denied claims that Musharraf had imposed martial law — direct rule by the army — under the guise of a state of emergency. He noted the prime minister was still in place and that the legislature would complete its term next week.

Commentators in local newspapers disagreed. "It is martial law," said the headline in Daily Times. "Gen. Musharraf's second coup," said the Dawn daily.

In Islamabad, phone service that was cut Saturday evening appeared to have been restored by Sunday morning. but transmissions by television news networks other than state-controlled Pakistan TV remained off the air.

Scores of paramilitary troops blocked access to the Supreme Court and parliament. Otherwise streets in the capital appeared calm, with only a handful of demonstrations. But one, attended by 40 people at the Marriott Hotel, was broken up by baton-wielding police.

"Shame on you! Go Musharraf go!" the protesters shouted as officers dragged some out of the crowd and forced them to the ground. Eight were taken away in a van.

Others were apathetic. Standing at on a dusty street corner in Islamabad, Togul Khan, 38, said he didn't care about the emergency declaration.

"What's the point of talking about this," said the day laborer, who was waiting to be hired for work. "For us, life stays the same, even when politicians throw Pakistan into the sky, spin it around and watch as it crashes back down to earth."

Western allies had urged Musharraf not to take authoritarian measures despite recent his country's recent turmoil.

Rice called for a return to democracy, as the American Embassy urged citizens in Pakistan to remain at home and defer nonessential travel.

In his televised address late Saturday, Musharraf, looking somber and composed, said Pakistan was at a "dangerous" juncture, and that its government was threatened by Islamic extremists who were "imposing their obsolete ideas on moderates."

The military ruler, wearing a black button-down tunic rather than his army uniform, also blamed the Supreme Court for tying the hands of the government by postponing the validation of his recent election. The court was expected to rule soon on opponents' claims that Musharraf's Oct. 6 victory was unconstitutional because he contested while army chief. He was elected by a Musharraf-led legislature.

Bhutto, who had traveled abroad following an Oct. 18 suicide bombing that narrowly missed her but killed 145 others, immediately returned to the southern city of Karachi declared Saturday the "blackest day" in Pakistan's history. "Judicial decisions have to be accepted even if they don't suit you," she said.

Analysts, meanwhile, said the imposition of emergency rule may only postpone Musharraf's political demise. "He's obviously not very popular, and it's not going to increase his popularity," said Rick Barton, a Pakistan expert at the Washington-based Center for International and Strategic Studies.

Musharraf issued two ordinances toughening media laws, including a ban on live broadcasts of "incidents of violence and conflict." Also, TV operators who "ridicule" the president, armed forces, and other powerful state bodies face up to three years in jail.

Associated Press writers Khalid Tanveer in Multan; Zarar Khan, Sadaqat Jan, Munir Ahmad in Islamabad; and Ashraf Khan in Karachi contributed to this report.