"Iran fired a Shahab-3 Tuesday," said the official, who spoke on condition of anonymity.

The missile test has not been announced by Tehran.

"It can always help Iran increase its confidence in the program," said a second defense official without commenting on whether a test had taken place.

The test comes amid a mounting diplomatic confrontation with Iran over a uranium enrichment program that the United States insists is part of a secret effort to develop nuclear weapons.

Iran insists its nuclear program is for peaceful purposes but has refused international appeals to stop.

The Shahab-3, which is modeled on the North Korean No-Dong missile, has a reported range of some 1,300 kilometers (800 miles), putting Israel, Afghanistan and US military installations in the region within reach.

Iran is reported to be working on extending the missile's range. An Iranian general in January said that the Shahab-3 was capable of striking targets 2,000 kilometers (1,200 miles) away.

This would be the about the ninth flight test of the missile since 1998, according to experts who have tracked the program.

"I think they will have high confidence that the missile will work by the time they have atomic bombs to put on it," said John Pike, executive director of GlobalSecurity.Org.

"They have been developing it in cahoots with Pakistan and North Korea. And Pakistan has been testing it as well," he said.

"It's a general rule of thumb for an American missile program that you would like to have about 20 developmental tests before you had confidence in the fly-ability of the thing, and between Pakistan and Iran's test I think they are pretty close to that."

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