Pakistan braced for protests against emergency rule on Monday, while President Pervez Musharraf faced mounting pressure from the United States to hold parliamentary elections in January.
Declaring an emergency on Saturday, General Musharraf cited spiraling militancy and hostile judges to justify his action.
Police detained opposition figures and lawyers -- between 400 and 500 according to Prime Minister Shaukat Aziz -- and placed reporting curbs on the media to stifle the risk of outrage spilling on to the streets.
Musharraf, who seized power in a coup in 1999, also suspended the constitution.
U.S. Secretary of State Condoleezza Rice expressed disappointment with Musharraf in terms seldom heard before from U.S. officials more accustomed to praising the Pakistani leader's support in the battle against al Qaeda.
"The United States has never put all of its chips on Musharraf," Rice said, urging Pakistan to get back on the road to democracy, and warning U.S. aid to its ally was under review. Washington has given Islamabad around $10 billion over the last five years.
Despite the detentions, a lawyers' movement that led the fight against Musharraf when he tried to sack the country's top judge earlier this year, was planning protests in front of courts in most major cities.
Lawyers, journalists, opposition politicians, and ordinary Pakistanis said they believed Musharraf's main motive in declaring emergency rule was to pre-empt the Supreme Court invalidating his re-election as president last month.
"Many people in Pakistan believe that it has nothing to do with stopping terrorism, and it has everything to do with stopping a court verdict that was coming against him," former Prime Minister Benazir Bhutto said on Sunday.
The Court had been due to reconvene on Monday to determine Musharraf's right to have stood for re-election while still army chief. But judges, including Chief Justice Iftikhar Chaudhry, have been sacked and all proceedings cancelled this week.
Nuclear-armed Pakistan's security has deteriorated sharply since July, when commandos stormed the Red Mosque in Islamabad to crush a Taliban-style movement.
Nearly 800 people have been killed in militant-linked violence since then, including more than 23 suicide attacks. Morale in the security forces is low.
On Sunday, a Pakistani Taliban group freed 211 soldiers humiliatingly captured on Aug. 30. They were exchanged for 25 prisoners held by the authorities, intelligence officials said.
While the United States wants Pakistan to go ahead with elections, which had been due in January, it does not want to jeopardize counter-terrorism efforts.
Prime Minister Aziz said that Pakistan was committed to holding elections, but he could not say when. He noted that under the terms of an emergency, parliament's term, due to expire this month, could be extended for a year.
Nawaz Sharif, the exiled prime minister Musharraf deposed in 1999, said he should quit for the sake of the country.
But Humayun Ansari, a 54-year-old business professor in Karachi, said that might make the situation even worse. "That would be an invitation for real, real trouble."
What Bhutto, who heads the largest opposition party, does next could be crucial. Musharraf allowed Bhutto back from eight years of self-imposed exile last month by granting her immunity against prosecution in old corruption cases.
Before Musharraf proclaimed emergency rule there had been talk that the two could share power after the elections, so long as he quit the army.