Asked on CNN television whether Washington had given Israel the go-ahead for such an attack, Obama said: "Absolutely not."

In the interview with the US network broadcast from Russia where he is on an official visit, Obama added that Washington could not "dictate" the security interests of other countries and would seek to settle the dispute through diplomacy.

"What is also true is, it is the policy of the United States to try to resolve the issue of Iran's nuclear capabilities," Obama said.

This would be achieved "through diplomatic channels," he said.

The remarks followed comments by Vice President Joe Biden over the weekend that the United States would not stand in the way of Israel in its response to Iran's nuclear ambitions.

"Israel can determine for itself... what's in their interest and what they decide to do relative to Iran and anyone else," Biden told ABC television's "This Week" program in an interview broadcast Sunday.

"We cannot dictate to another sovereign nation what they can and cannot do when they make a determination -- if they make a determination -- that they're existentially threatened," Biden said.

Obama on Tuesday stressed that he wanted first to see progress on diplomacy, as the United States attempts to end Tehran's controversial nuclear drive.

"I think Vice President Biden stated a categorical fact, which is that we can't dictate to other countries what their security interests are," the US president said.

Obama said that "the United States reserve(s) the right, and I as commander-in-chief reserve the right, to take whatever actions are necessary to protect the United States."

Asked about Iran at an event Tuesday in Washingtion, the top US military officer, Admiral Mike Mullen, said Tehran could have an atomic bomb within one to three years and that such a development risked unleashing a nuclear arms race in the Middle East.

If Iran secured a nuclear arsenal it "would be potentially very destabilizing," Mullen told an audience at the Center for Strategic and International Studies.

"My concern is that, you know, the clock has continued to tick," he said.

Saying Israel viewed a nuclear-armed Iran as an existential threat, Mullen spoke of the "criticality in my view of solving this before Iran gets a nuclear capability or that anyone would, you know, take action to strike them."

Mullen, who is chairman of the US Joint Chiefs of Staff, said the focus was on diplomatic efforts but echoed Obama's comments, refusing to rule out military options.

"There is a great deal that certainly depends on the dialogue and the engagement, and I think we need to do that with all options remaining on the table, including certainly military options," he said.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.