A key concern is the imposition of sanctions by major aid donors, including the US and Japan, which will cost Pakistan billions of dollars.

BBC Correspondent in Islamabad Owen Bennett-Jones: 'Pakistan has not said the programme is over'

The decision to go ahead with the tests followed explosions earlier this month by India.

Meanwhile, US officials believe Pakistan may be preparing yet another nuclear test.

The officials, who would not be identified, said American spy satellites monitoring a site in Pakistan had picked up signs of preparations; one official said a sixth nuclear test could be readied in a couple of days.

However, the Pakistani Finance Minister Sartaj Aziz said his country had no plans for further tests at the moment.

State of emergency

Immediately after the tests on Thursday, Pakistan's Prime Minister Nazwaz Sharif told the nation that the imposition of sanctions will cause difficulties for Pakistan.

Prime ministerial warnings came immediately

A state of emergency has been declared which will enable the government to introduce austerity measures without the risk of court challenges.

Restrictions have already been imposed on foreign exchange transactions, and banks are closed today to prevent the withdrawal of deposits.

Pakistan's information minister has said the state of emergency does not mean that the army will be on the streets, but he was unable to say how long it will last.

Celebrations continue

The nuclear blasts have been widely welcomed inside Pakistan where celebratory rallies are planned today.

Friday's newspapers in Pakistan have celebrated the tests with headlines such as "Pakistan levels the score".

Tests 'deplored'

The Indian Prime Minister, Atal Behari Vajpayee, said Pakistan's nuclear tests vindicated India's decision to conduct tests of its own earlier this month.

In the rest of the world, there was near universal condemnation of Pakistan.

President Clinton: Pakistan has lost a 'priceless opportunity'

President Clinton said: "I deplore the decision. By failing to exercise restraint Pakistan has lost a truly priceless opportunity ... two wrongs don't make a right."

He said that America would impose sanctions on Pakistan in the way it imposed them on India as punishment for the nuclear tests it conducted earlier in the month.

BBC correspondent Ben Brown reports on the nuclear rivalry on the subcontinent

"It is now more urgent than it was yesterday that both India and Pakistan renounce further tests and sign the comprehensive test ban treaty ... and reverse the dangerous arms race," he said.

Describing the tests as "extremely deplorable" Japanese officials have decided to impose economic sanctions on Pakistan as strict as those imposed in India.

Japan is Pakistan's biggest aid donor providing 32bn yen in loans and 5.7bn yen in grants-in-aid in 1997.