The devices were detonated under the desert wastes of Baluchistan, near the Iranian border and were a riposte and a warning to India, whose five tests earlier this month stunned the world.
Hours later President Rafiq Tarar declared a state of emergency citing a "threat by the external aggression to the security of Pakistan". The terse announcement did not identify the aggressor but Pakistan accused India of threatening to attack its nuclear installations.
Reaction was swift and severe. President Clinton condemned the decision as a "lost opportunity" and said: "We have no choice but to impose sanctions. Two wrongs don't make a right and it is now more urgent that it was yesterday that both Pakistan and India renounce further tests, sign the Comprehensive Test Ban Treaty and take decisive steps to reduce tensions in South Asia and reverse the dangerous arms race."
US government officials said later that they believed that Pakistan was preparing for a second test within the next few days.
Robin Cook, the Foreign Secretary, said Britain was "dismayed" by the nuclear tests carried out by Pakistan. "It accentuates our grave concern about the increased risk of nuclear and missile proliferation in South Asia, and of escalating tension in that region," he said.
In Delhi, the Lower House of Lok Sabha, India's parliament, adjourned in shock and consternation when the news arrived. After an emergency meeting the Prime Minister, Atal Behari Vajpayee, said India was "ready to meet any challenge".
Soon after the announcement, Pakistani prime minister Nawaz Sharif said on television that India's detonations three weeks ago had "violently tilted the balance of power in the region," and India's deployment of long-range Prithvi missiles against Pakistan was a serious threat.
The "lacklustre" response of the West to India's move had only served to embolden India, he added. "We will have sanctions, we will have difficulties," he went on, "but if you have the strength, there is no way we can fail."
Preparing the nation for a period of austerity, he announced that the government would sell off many offices and buildings and use the money to help the nation through the tough times ahead.
Canada recalled its ambassador to Pakistan and urged the World Bank to defer its projects there following the nuclear explosions. "I think it's a very sad development," said the Canadian Prime Minister Jean Chretien. He had personally urged Mr Sharif not to proceed with the nuclear tests.
The EU condemned the tests and promised to "take all necessary measures" if Pakistan and India did not sign the relevant nuclear non-proliferation treaties.
A NATO spokesman said that Pakistan's action had caused "dismay", as all the allies had called for Pakistan to exercise restraint.
"Both India and Pakistan risk becoming outcasts in the international community," he added.
Kofi Annan, the United Nations General Secretary, echoed the call for both the Indians the Pakistanis to sign the test ban treaty and pledge not to use nuclear weapons against each other.
Pakistan's tests, which, unlike India's, were closely monitored by US intelligence, had been preceded by a fortnight of anguished debate.
With its economy in far weaker shape than India's, Pakistan is in no position to shrug off the certainty of international sanctions. In particular the withdrawal of Japanese and American aid, and the possible cut-off of loans from the World Bank and the IMF, will throw the nation's economy into disarray.Reuse content