"Pakistan's tests do not pose any new threat to our national security," Atal Behari Vajpayee told the upper house of parliament. "We do not intend to join an arms race."

The Defence Minister, George Fernandes, earlier dismissed news of the Pakistani tests as predictable.

He said that Indian seismic centres had recorded only one underground nuclear blast by Pakistan, with only a fraction of the force of India's explosions.

Indian Defence Minister George Fernandes says 'we will do whatever necessary to defend our national security'

"If there were more tests than one, then the tests were simultaneous and successive tests were of smaller yield than the first one," he said.

He also said that observations of Pakistan's tests, recorded at multiple centres, indicated a likely yield of about 10 kilotonnes.

India says its five explosions in mid May yielded the explosive equivalent of about 60 kilotonnes of conventional explosive.

The US Defence Department said the United States had also closely monitored Pakistan's tests, and there was no immediate evidence they included a powerful thermonuclear explosion, the reaction produced in a hydrogen bomb.

Uproar in India's parliament

As news of Pakistan's tests on Thursday broke, there was an uproar in the Indian parliament.

BBC's Daniel Lak says ministers were relieved by Pakistan's tests

Amid rowdiness and jeering, the Indian Prime Minister Vajpayee appealed for consensus, and said the tests brought the nuclear programme they long suspected in Pakistan out into the open.

"India is ready to meet any challenge. The people must stand united to face the new situation," he said.

However, opposition MPs accused the prime minister of setting off a regional arms race. The main opposition Congress party said in a statement that Pakistan's tests were a 'grave development', and called for restraint from the government.

Meanwhile, a leading member of the ruling BJP coalition, Mohan Guruswamy , implied that China was a much greater threat than Pakistan.

"Pakistan is not the most major of our problems. It is probably the least of our problems. We have other challenges. We have a neighbour in the north who has a large nuclear arsenal."