"Pakistan's interest would be served by a prompt return to civilian rule and restoration of the democratic process," he said on Wednesday.

"I urge that Pakistan move quickly in that direction."

The US ambassador to Pakistan, who was away at the time of the military takeover, is now heading back there, said Mr Clinton, to "underscore my view directly to the military authorities and to hear their intentions".

A senior government official told Associated Press on condition of anonymity that US intelligence had warned for several months of the possibility of a military takeover.

US State Department spokesman James Rubin: "The spirit and the letter of the constitution should be respected"

"It was not a surprise at all that it happened," although the timing of Tuesday's takeover was not known, the official said.

Only three weeks ago, US officials expressed concern about a possible military coup because of political turmoil and opposition demands that Mr Sharif should leave office.

EU's demand

The European Union was quick to react to the takeover.

It issued a statement calling for the return of civilian rule, and suspended the signing of a partnership agreement with Pakistan.

Current EU president Finland said: "The EU can in no circumstances approve extra-constitutional and non-democratic means in any country and therefore urges the Pakistani military to respect democracy and the parliamentary process."

The Commonwealth - a grouping of former British territories - warned that it may suspend Pakistan if the military does not hand over power quickly.

Secretary-General Emeka Anyaoku said that what had happened "flies in the face" of democracy and "isolates the Pakistani regime".

Other reaction

Among other countries outside the region expressing their concern:

• Germany called for respect for constitution
• UK condemned unconstitutional action
• President Obasanjo of Nigeria broke off military relations with Islamabad.
• Australia called for "earliest restoration of democracy"
• Japan said it hoped the coup could be resolved peacefully
• Thailand said it could be a setback for the region's nuclear non-proliferation hopes