Washington - Tensions between the White House and Benjamin Netanyahu intensified Wednesday as top administration officials condemned the Israeli prime minister's plan to address Congress next week, while Netanyahu accused six world powers, including the United States, of "giving up on their commitment" in negotiations to prevent Iran from obtaining a nuclear weapon.

The unusually public spat marked one of the lowest points in a relationship that has long bonded the two countries. Although the new round of recriminations reflected the frosty personal relations between President Barack Obama and Netanyahu, it came at a critical juncture in multilateral talks designed to prevent Iran from using a civilian program to develop a nuclear weapon.

The prime minister has said that unfolding deal - to which Iran has not yet agreed - could pose an existential threat to the Jewish state. Obama, however, considers a deal a potential legacy that could ease nuclear tensions, lift trade restrictions on Iran and alter the region's strategic calculus.

Congressional Democrats have been caught in the middle of the dispute. On Wednesday, Sen. Timothy Kaine, D-Va., became the fourth senator to say he would skip Netanyahu's speech in Congress next week, calling its timing "highly inappropriate." Several members of the House also have said they would boycott the speech.

The latest volley of high-level criticism began when national security adviser Susan Rice, appearing on "Charlie Rose" on Tuesday night, condemned Netanyahu's decision to accept the invitation of House Speaker John Boehner, R-Ohio, to appear at a joint session of Congress shortly before the Israeli elections.

By bypassing the White House, dealing only with GOP leaders and scheduling the speech just before Israelis vote, Netanyahu had "injected a degree of partisanship, which is not only unfortunate," Rice said. "I think it's destructive of the fabric of the relationship."

At a Likud political convention in the Maale Adumim settlement just east of Jerusalem, Netanyahu fired back. "I respect the White House and the president of the United States, but on such a critical topic that could determine whether we exist or not, it is my duty to do everything to prevent this great danger to the state of Israel," Netanyahu said.

Congress could play a critical role in the Iran talks. It is weighing whether to add new sanctions to the harsh ones already in place. The existing sanctions, and those adopted by the European Union, are widely viewed as having helped push Iran to the bargaining table. But Obama has vowed to veto any new sanctions and has urged Congress to wait at least another month for the outcome of the current negotiations. Obama has said that if the talks fail, he will move to tighten economic restrictions.

Secretary of State John Kerry defended the administration's conduct of negotiations in testimony before the House Foreign Affairs Committee - and took a swipe at Netanyahu.

"I'll tell you Israel is safer today with the added time we have given and the stoppage of the advances of the Iranian nuclear program than before," Kerry said. Referring to the accord that slightly eased sanctions while negotiations took place, he said: "We got that agreement - which by the way the prime minister opposed. He was wrong. And today he's saying we should be extending that interim agreement."

No love has been lost between Obama and Netanyahu.

"This is clearly the most dysfunctional relationship between an American and Israeli leader," said Aaron David Miller, a vice president at the Wilson Center and a former U.S. negotiator and adviser to both Republican and Democratic administrations. Moreover, he said, "the durability is troubling." He said that earlier tensions preceded incremental peace accords but that Obama and Netanyahu remain far apart on basic issues and that Kerry's efforts to bring Israel and Palestinians together failed.

Now their personal tensions have put Democratic lawmakers in awkward positions that threaten bipartisanship when it comes to Israel.

Democrats have been wrestling over whether to boycott the speech, as senior Obama administration officials plan to do. Because Netanyahu did not arrange his visit through the White House, Obama has said that he will not meet with him and Vice President Joe Biden has made plans to travel abroad.

"There is no reason to schedule this speech before Israeli voters go to the polls on March 17 and choose their own leadership," Kaine said in a statement Wednesday. "I am disappointed that, as of now, the speech has not been postponed. For this reason, I will not attend the speech."

Kaine joins Senate colleagues Patrick Leahy, D-Vt., Bernard Sanders, I-Vt., and Brian Schatz, D-Hawaii, in skipping the prime minister's address.

But major Jewish American organizations, which say they didn't know about Netanyahu's plans, said lawmakers should put aside the protocol issues and listen to the premier's message on the Iran talks.

Sens. Diane Feinstein, Calif., and Richard Durbin, Ill., invited Netanyahu to attend a separate event with Democratic lawmakers but he declined. In a letter, he said that it "could compound the misperception of partisanship regarding my upcoming visit."

Sen. Orrin G. Hatch, R-Utah, said that "it's unseemly what the Democrats have done to try and make this a political issue. I think the president has acted like an oaf, an oaf. O-a-f. . . . I don't even want to get into it, I'm just mad."

Meanwhile, leaked details about Iran nuclear negotiations have made many lawmakers more interested in what Netanyahu has to say.

"I think his voice will resonate more credibly if that's the deal that's in the making," said Abraham Foxman, president of the Anti-Defamation League. "Both the president and prime minister share the goal of preventing Iran from going nuclear. How to get there is what separates them."

Sen. Jack Reed, D-R.I., one of Obama's strongest allies on the Hill, plans to attend Netanyahu's speech. "I'm interested in what the prime minister is going to say," Reed said. "I think it's already been made an unnecessarily complicated political issue, but there is still this need to learn as much as we can about the situation."

Many will hear Netanyahu on Monday, when he addresses the annual American Israel Political Action Committee convention. AIPAC expects 16,000 people to attend, including about 50 lawmakers.