Vice President Joe Biden on Monday defended President Obama's pursuit of diplomatic negotiations with Iran in a speech to the liberal pro-Israel group J Street, saying that the U.S. would “not tolerate” a nuclear-armed Tehran.

In a wide-ranging foreign policy speech, Biden reaffirmed the U.S. commitment to Israel, which he said faced an “existential threat” from the Iranian regime.

Biden praised Obama’s handling of Iran, saying that he had “rallied the whole world even though skeptics thought it would not work to get the U.N. behind the most effective sanctions regime in all of history.”

Biden keynote address at the annual meeting of the liberal pro-Israel advocacy group made him the highest-profile administration official to speak to the organization, which has positioned itself as a rival to the more conservative and well-established American Israel Public Affairs Committee.

Biden’s remarks came hours after Israeli Prime Minister Benjamin Netanyahu visited with President Obama at the White House, as the administration seeks to assuage Israeli concerns over U.S. diplomatic talks with Iran.

Obama on Friday spoke with newly-elected Iranian President Hassan Rouhani, the first such contact between the two countries leaders since 1979. The White House believes the talk could set the stage for a deal aimed at halting Iran's nuclear weapons program.

Netanyahu, however, has urged caution, warning that Tehran may be stalling for time as it continues to pursue nuclear arms. Israel has called on the U.S. to maintain sanctions against Iran.

Biden said the existing sanctions had a “profound impact” and that the U.S. would insist on “concrete steps” actions proving Iran intended to abandon pursuit of nuclear arms.

Lawmakers, though, are divided on the prospect of talks with Iran.

Sen. John McCain, R-Ariz., on Monday told the Washington Examiner that Obama's approach should be "don't trust, but verify."

"So far they've done nothing but talk," he said of Iran.

But Sen. Dianne Feinstein, D-Calif., called the talks a "breath of fresh air."

"What really upsets me is that a certain section of people on both sides are immediately throwing rocks at it," she said. "Before this, we haven't talked in 35 years on a presidential level – and it looks like that's going to start. And I personally view that as a very positive sign."

The vice president also defended Obama’s decision to pursue a diplomatic solution for disarming Syrian leader Bashar Assad’s chemical arsenal.

Biden also expressed caution for greater U.S. involvement in that country’s brutal 2-year civil war.

“A civil war in Syria does not lend itself to U.S. military intervention.” he said.

Biden also said that the “vast majority” of Israelis and Palestinians supported a peaceful solution to their decades long conflict.

Secretary of State John Kerry has launched a renewed effort to push Israel and the Palestinian leadership back to the negotiating table.

Susan Crabtree contributed.