The council, which was called into emergency session for the second day running, expressed growing concern at the risk of a nuclear arms race.

UN correspondent Rob Watson : "snub to security council"

It wants Islamabad to declare a moratorium on nuclear tests and experiments on delivery systems.

The council, meeting in a rare weekend session, repeated calls on Pakistan and India to sign the Comprehensive Test Ban Treaty, which along with the 1970 Nuclear Non-Proliferation Treaty form the basis of global agreements to curb nuclear weapons.

They will examine a resolution threatening unspecified measures to punish the two countries.

In other reactions:

India said it would not respond to Pakistan's latest nuclear explosion with further tests of its own.

Officials in Delhi said India would continue to observe its voluntary nuclear moratorium, and repeated that the government was willing to discuss turning this into a formal obligation.

A foreign ministry statement said: "The developments are on expected lines.

"We have been monitoring Pakistan's clandestine programme very closely and all this is factored into our defence policy."

Robin Cook: "flagrant disregard" for international opinion

In Britain, the Foreign Secretary Robin Cook accused Pakistan of acting with "flagrant disregard" for international opinion by carrying out the latest test.

Mr Cook said the new test did nothing to enhance Pakistan's security, but further escalated concerns about an arms race in south Asia.

In the United States, President Bill Clinton condemned Pakistan and said India and Pakistan were contributing to a "self-defeating cycle of escalation".

"These tests can only serve to increase tensions in an already volatile region," he said.

In Germany, Foreign Minister Klaus Kinkel condemned Pakistan's latest test and urged the UN Security Council to meet immediately to try to stop the "crazy escalation" in South Asia's arms race.

Japan has indicated it may recall its ambassador to Pakistan, a Japanese news agency reported.

Klaus Kinkel: tests a "crazy escalation"

The Japanese Government strongly denounced the testing, calling Pakistan's move "an act that challenges and runs against the nuclear non-proliferation movement, ignoring the international public movement".

In Australia, Prime Minister John Howard condemned the new test as "dismaying". He said the test compounded the outrage in what was becoming a dangerous game.

France called on both Pakistan and India to sign a global treaty banning nuclear tests.

A Foreign Ministry statement said: "France condemns the new tests which Pakistan has just carried out and calls on Pakistan to put a definitive end to such tests.

"France renews its appeal to Pakistan and to India to quickly, unconditionally sign the Nuclear Test Ban treaty and participate in negotiations towards a treaty to ban the production of fissile materials aimed at producing nuclear arms."