The US is to review its multi-billion dollar aid package to Pakistan after President Pervez Musharraf declared a state of emergency on Saturday.
Police have kept tight control over protests in Islamabad
US Secretary of State Condoleezza Rice stressed that some aid was directly linked to tackling al-Qaeda and Taleban militants - a major US priority.
The UK, another major donor, says it is examining whether the emergency will affect its aid to Pakistan.
Mr Musharraf said he was imposing the emergency in order to curb extremism.
Islamabad has suggested parliamentary polls scheduled for January could be delayed by up to a year.
Rights have been suspended, media have been restricted and at least 400 people arrested under the emergency decree.
Prime Minister Shaukat Aziz said the emergency would last for "as long as is necessary".
Lawyers' groups have called for a nationwide boycott of the courts on Monday and there have been small protests in the capital, where police and security forces are on the streets surrounding key sites.
Pakistan has received at least US$10bn from the US since it became a close ally in President George W Bush's "war on terror" in 2001.
Constitutional safeguards on life and liberty curtailed
Police get wide powers of arrest
Suspects can be denied access to lawyers
Freedom of movement restricted
Private TV stations taken off air
New rules curtail media coverage of suicide bombings or militant activity
Chief justice replaced, others made to swear oath of loyalty
Supreme Court banned from rescinding emergency order
"Some of the aid that goes to Pakistan is directly related to the counter-terrorism mission," Ms Rice, who is visiting the Middle East, told reporters.
"We just have to review the situation."
She added that she did not expect the US "to ignore or set aside [its] concerns about terrorism".
The scale of US aid shows just how important Gen Musharraf is to the Americans as a bulwark against Islamic militancy, the BBC's Sebastian Usher notes.
Condoleezza Rice's comments are unusually critical but they do not suggest that the Bush administration is likely to take any concrete action against the man it has long seen as a key regional ally any time soon, he adds.
Pakistan is due to receive £480m ($1bn) in assistance from Britain between 2008 and 2011, according to the UK's Department for International Development.
A Foreign Office spokesman said London would consider the implications of the new situation on its programmes in Pakistan but declined to say when such a review would take place or if it would affect the sums involved.
Reacting to news of the US aid review, Republican presidential hopeful Fred Thompson called for a "hardball" approach with Gen Musharraf, short of cutting aid.
Benazir Bhutto returned to Pakistan after the emergency
"We need to understand that this is a nuclear country," he said on NBC television.
"We could face a real nightmare scenario by seeing these radical elements, these terrorist sympathizers, take control of that government."
Gen Musharraf says he declared the emergency to stop Pakistan "committing suicide", because the country was in a crisis caused by militant violence and an unruly judiciary.
The move came as the Supreme Court was due to decide whether Gen Musharraf was eligible to run for re-election last month while remaining army chief.
Fears were growing in the government that the court could rule against Gen Musharraf.
Benazir Bhutto, a political rival of Gen Musharraf, told US TV channel ABC News that many people believed the emergency was aimed at "stopping a court verdict that was coming against him".
Nawaz Sharif, another rival who is exiled in Saudi Arabia, told the BBC World Service he would be part of a nationwide campaign against Gen Musharraf's actions.
"We, together with other political parties who believe in democracy and the restoration of the rule of law, are going to launch a decisive movement against Musharraf's high-handedness, and undemocratic actions," he told the World Today.
There were few acts of protest on the streets of Pakistan's big cities on Sunday though police did break up a brief rally by a few dozen people near parliament in Islamabad.
Tough new media restrictions are controlling the news available throughout Pakistan: all non-state TV stations and some radio channels have been taken off the air, as have international services such as BBC World TV.
Independent newspapers have been allowed to continue publishing, but Gen Musharraf's decree severely limits what they can report.