President Clinton has deplored the decision by Islamabad to go ahead with the tests, saying this left the United States with no choice but to impose sanctions on Pakistan.

He said that by responding in kind to the Indian nuclear tests, Pakistan had lost a priceless opportunity to strengthen its political standing in the eyes of the world.

Mr Clinton added it was now more urgent than ever that both countries renounce further tests and reverse a dangerous arms race.

This call was echoed by the United Nations Secretary-General, Kofi Annan, who said both countries should immediately sign the nuclear test ban treaty.

Russia also expressed deep concern, while Britain condemned the tests.

NATO has urged restraint by both India and Pakistan.