Israeli Prime Minister Benjamin Netanyahu warned the United States on Monday that the nuclear deal it is negotiating with Iran could threaten Israel's survival and insisted he had a "moral obligation" to speak up about deep differences with President Barack Obama on the issue.

In a preview of a planned address to Congress on Tuesday that has already imperiled U.S.-Israeli ties, Netanyahu voiced fears that talks between Iran and world powers would allow Tehran to become a nuclear-armed state and said this must not happen.

"As prime minister of Israel, I have a moral obligation to speak up in the face of these dangers while there's still time to avert them," Netanyahu told a cheering audience at the annual conference of the American Israel Public Affairs Committee (AIPAC), the largest U.S. pro-Israel lobby.

At the same time, Netanyahu sought to ease U.S.-Israeli tensions, saying the relationship between his country and the United States was "stronger than ever" and would continue to improve. He said the widespread characterizations of fraying relations were "not only premature, they're just wrong."

The long-strained personal relationship between Obama and Netanyahu has sunk to a new low over the Israeli leader's planned speech to a joint meeting of Congress on Tuesday, just weeks before an end-of-March deadline for a framework accord between Iran and world powers.

Netanyahu is expected to press U.S. lawmakers to block a deal with Iran that he contends would endanger Israel's existence but which Obama's aides believe could be a signature foreign policy achievement for the president.

The invitation to Netanyahu was orchestrated by Republican congressional leaders with the Israeli ambassador without advance word to the White House, a breach of protocol that infuriated the Obama administration.

Obama has said he will not meet with Netanyahu during this visit, on the grounds that doing so just two weeks before Israeli elections could be seen as interfering.

The partisan nature of this dispute has turned this into the worst rift in decades between the United States and Israel, which normally navigates carefully between Republicans and Democrats in Washington.