The assertion went far beyond what rocket experts have established about Iran’s missile capabilities, and American officials questioned its accuracy.

The Israeli official, Moshe Yaalon, a deputy prime minister and minister for strategic affairs, said the explosion, at a Revolutionary Guard missile base, hit a system “getting ready to produce a missile with a range of 10,000 kilometers.”

“That’s the Great Satan,” he said, invoking the term Iran often uses to refer to the United States. “It was aimed at America, not at us.”

Mr. Yaalon was trying to make the point that the Iranian nuclear program is not a threat only to Israel but, as he put it, “a nightmare for the free world.” He said that it was a concern to Arab states as well as to the United States and Israel.

American officials said they believed Mr. Yaalon’s assertions were at best premature, and at worst badly exaggerated.

Speaking on condition of anonymity because assessments of Iran’s missile capabilities are largely classified, the officials said that Iran may harbor the ambition of having missiles that can reach the United States, but it is nowhere close to achieving such a capability. They declined to say what kind of missile work was being done at the base where the explosion took place.

Today, the maximum range of Iran’s known ballistic missiles is roughly 1,200 miles, rocket experts say. That means they could reach targets throughout the Middle East, including Israel, as well as all of Turkey and parts of Eastern Europe.

Iran is known to be working on missiles with a range of 2,000 miles, which are considered medium range. The United States has defined long-range or intercontinental ballistic missiles as having ranges greater than 3,400 miles.

A range of 10,000 kilometers, slightly more than 6,200 miles, would let a missile fired from Iran fly halfway around the globe to reach the United States.

Mr. Yaalon’s comments came in an address to a public conference held annually outside Tel Aviv that examines Israel’s security challenges.

Mr. Yaalon, who was in the United States last week to discuss Iran’s nuclear program with American officials, also said in his remarks that Turkey had been helping Iran circumvent international sanctions by allowing it to use its banking system. He also argued that all of Iran’s nuclear sites could be hit with Western weapons.

“We need a credible military option,” he said. “The Iranians understand the West has capabilities but as long as the Iranians don’t think that the West has the political stomach and determination to use it, they will not stop. Currently they don’t think the world is determined.”

Earlier, Maj. Gen. Aviv Kochavi, the chief of Israeli military intelligence, told the audience that he believed crippling sanctions could persuade the Iranian government to abandon what he believes is its determination to build a nuclear weapon. He said if Iran chose to build a bomb, it would take it about a year.

General Kochavi also estimated that Israel faced about 200,000 missiles and rockets aimed at it from its enemies.

Defense Secretary Leon E. Panetta, speaking to reporters at a NATO meeting in Brussels, declined to comment on a column by David Ignatius the Washington Post that reported that Mr. Panetta believed there was a “strong likelihood” that Israel would strike Iran in April, May or June.

Mr. Panetta would only say that “Israel has indicated that they’re considering this and we have indicated our concerns.”

William J. Broad contributed reporting from New York, Elisabeth Bumiller from Brussels and David E. Sanger from Washington.