CBS News National Security Correspondent David Martin reported that U.S. intelligence, which has been watching the test site with spy satellites, only has evidence of three underground blasts, but whatever the number, Pakistan's ambassador to the U.S. said that after India set off five nuclear devices earlier this month his country had no choice.
There are news reports Pakistan is arming its missiles, but the ambassador insists his country has made no decision to do that.
Pakistan may not be through testing yet. Spy satellites have spotted the Pakistanis making preparations at a second test site, and U.S. intelligence believes more nuclear tests are likely.
CBS News Correspondent Scott Pelley reports from Washington that a senior official says the situation now is one of immense danger with global implications. The nuclear escalation is also a grave disappointment to the president.
Mr. Clinton was on the phone after midnight today trying to convince the Pakistani prime minister to wait. Prime Minister Nawaz Sharif did not tell Mr. Clinton that the bombs would go off in five hours.
President Clinton said on Thursday afternoon, "Pakistan lost a truly priceless opportunity to strengthen its own security to improve its political standing in the eyes of the world. And although Pakistan was not the first to test, two wrongs don't make a right."
Mr. Clinton immediately ordered the same economic sanctions that he imposed against India this month. Now the White House strategy is to convince both countries not to deploy their atomic weapons.
U.S. intelligence spotted the test immediately at 6:41 this morning. Less than two hours later, on the phone Mr. Clinton told Sharif he'd made exactly the wrong decision.
"I cannot believe that we are about to start the 21st century by having the Indian sub-continent repeat the worst mistakes of the 20st century," said the President.
White House officials are looking for a way to lessen the sanctions impact and try to convince Pakistan to end its testing now. There is sympathy for Pakistan. Sharif was under enormous political pressure. The economic sanctions will hurt struggling Pakistan much harder than India.
Since it detonated five nuclear devices, India has been under economic sanctions, most recently this week when the World Bank indefinitely postponed a decision on whether to extend more than $800 million in loans to the impoverished nation.
On Wednesday, Pakistan Foreign Minister Gohar Ayub Khan said the test was inevitable, and Prime Minister Nawaz Sharif was just waiting to pick a time.
U.S. intelligence officials concluded Tuesday that Pakistan completed most of the preparation for a test in the western Chagai Hills, 30 miles from the border with Iran.
Pakistan and India have fought three wars since 1947, when the subcontinent gained independence from Britain: in 1948, 1965, and again in 1971.