Biden's remarks suggested a tougher U.S. stance against Iran's nuclear ambitions. Nonetheless, administration officials insisted his televised remarks yesterday reflected the U.S. view that Israel has a right to defend itself and make its own decisions on national security.

In an interview on ABC's This Week, Biden also said the U.S. offer to negotiate with Tehran on its nuclear program still stood. Some thought the administration's approach might change in light of the Iranian government's harsh crackdown on protesters after the June 12 presidential election. Opponents of the ruling authorities contended that the vote was rigged against them.

"If the Iranians respond to the offer of engagement," Biden said, "we will engage."

It was after meeting Israeli Prime Minister Benjamin Netanyahu at the White House on May 18 that President Obama said it should be clear by year's end whether Iran was open to direct negotiations.

Biden was asked whether Netanyahu was taking the right approach by indicating Israel would take matters into its own hands if Iran did not show a willingness to negotiate by the end of the year.

"Israel can determine for itself - it's a sovereign nation - what's in their interest and what they decide to do relative to Iran and anyone else," Biden replied. He added that this was the case, "whether we agree or not" with the Israeli view.

Biden was then asked more pointedly whether the United States would stand in the way if the Israelis, viewing the prospect of an Iranian nuclear bomb as a threat to the existence of the Jewish state, decided to launch a military attack against Iranian nuclear facilities.

"Look, we cannot dictate to another sovereign nation what they can and cannot do," he said.

Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said yesterday that he had been concerned "for some time . . . about any strike on Iran." Speaking on CBS's Face the Nation, he said that military action should not be ruled out and that a nuclear-armed Iran is a highly troubling prospect.

In Jerusalem, the Israeli government had no comment. The Netanyahu government has said in the past that it preferred to see Iran's nuclear program stopped through diplomacy, but has not ruled out a military strike.

White House spokesman Tommy Vietor said Biden was not signaling any change of approach on Iran or Israel. "The vice president refused to engage hypotheticals, and he made clear that our policy has not changed," Vietor said. "Our friends and allies, including Israel, know that the president believes that now is the time to explore direct diplomatic options."

There are many reasons for Washington to oppose an Israeli attack on Iran now, including the presence in neighboring Iraq of about 130,000 U.S. troops, who could become targets of Iranian retaliation.