The Obama administration has boosted U.S. defense ties to Israel and will close ranks with its ally against any threat from a nuclear-armed Iran, Vice President Joe Biden said on Monday ahead of a trip to Israel.

Biden, the most senior U.S. official to visit since Israel President Barack Obama took office in January 2009, is widely expected to caution his hosts not to attack Iran pre-emptively while world powers pursue fresh sanctions against Tehran.

In an interview with the biggest-selling Israeli newspaper Yedioth Ahronoth, Biden emphasized Washington's efforts to drum up greater international diplomatic pressure on the Iranians, as well as unilateral measures imposed by the U.S. Treasury.

Asked about the prospect of an Israeli attack, he said:

Though I cannot answer the hypothetical questions you raised about Iran, I can promise the Israeli people that we will confront, as allies, any security challenge it will face. A nuclear-armed Iran would constitute a threat not only to Israel -- it would also constitute a threat to the United States.

The Obama administration, Biden said, gives Israel annual military aid worth $3 billion. We revived defense consultations between the two countries, doubled our efforts to ensure Israel preserves its qualitative military edge in the region, expanded our joint exercises and cooperation on missile-defense systems.

Israel, which is believed to have the region's only atomic arsenal, bombed Iraq's nuclear reactor in 1981 and, in 2007, launched a similar sortie against Syria. But many analysts believe its forces are too small to deliver more than disruptive strikes against Iran's distant, numerous and fortified sites.

Those tactical challenges, and U.S. reluctance to see a new regional war, has led some analysts to predict Israel will eventually come round to a strategy of containing Iran -- which denies its controversial uranium enrichment is for bombs.

Biden, who arrives in Jerusalem on Monday and departs Israel on Thursday, was not expected to take part in indirect Israeli-Palestinian talks that would be spearheaded by Obama's special envoy, George Mitchell, and could be announced during his visit, although he will be briefed on them.

U.S.-Israeli tensions flared over Obama's early push for a complete freeze to Jewish settlement in the West Bank, where Palestinians seek statehood as part of a future peace accord.

Obama has at least temporarily backed off, embracing a more limited, 10-month moratorium on new building announced by Israeli Prime Minister Benjamin Netanyahu in November.

Many Israelis are distrustful of Obama's outreach to the Muslim world, a priority he highlighted with high-profile visits to Egypt and Saudi Arabia, and, later this month, to Indonesia.

We certainly believe that when the United States effectively builds bridges with Muslim communities, this allows us to promote our interests, including interests that Israel benefits from, Biden told Yedioth.

The construction freeze was a unilateral decision by the Israeli government, and it is not part of an agreement with the American administration or with the Palestinians, he said.

It is not everything that we wanted, but it is an important action that has significant impact on the ground.

(Writing by Dan Williams; Editing by Jon Hemming)

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