WASHINGTON: Israeli Prime Minister Benjamin Netanyahu said Monday that diplomacy has so far failed to deter Iran from pursuing its nuclear program, warning the Islamic republic was getting closer to crossing a crucial "red line."

"Iran enriches more and more uranium, it installs faster and faster centrifuges," and it is "running out the clock" on diplomatic efforts to prevent it from obtaining a nuclear capability, Netanyahu said.

"We have to stop its nuclear enrichment program before it's too late," he warned in a speech via satellite from his office in Israel to the American Israel Public Affairs Committee, the largest pro-Israel lobby in the United States.

The Israeli prime minister warned that leaders in Tehran had opted to "just grit their teeth" through punishing international sanctions and pursue their nuclear plan, come what may.

"It's still not crossed the red line I drew with the United Nations last September," Netanyahu said, referring to the point at which Israel believes Iran would be able to build a nuclear bomb.

"But Iran is getting closer to that red line, and it is putting itself in a position to cross that line very quickly once it decides to do so."

With diplomacy failing as yet to bring about any solution to the crisis, Netanyahu stressed that Iran's leaders have "used negotiations, including the most recent ones, to buy time to press ahead with its nuclear program."

It was time to flex muscle, Netanyahu suggested. There must be "a clear and credible military threat if diplomacy and sanctions fail."

Netanyahu won re-election earlier this year but has so far struggled to scrape together a coalition. But he told the AIPAC audience that "I intend to form a strong and stable government in the days ahead."

One of its first duties he said would be hosting President Barack Obama on an official visit later this month -- his first as US commander in chief.

The two leaders would discuss Iran as well as Syria, where a civil war is raging against strongman Bashar al-Assad's regime.

Netanyahu said his own struggle to cobble together a government prevented him from traveling to Washington for AIPAC, as he has done in the past.

But the political strain in Israel is not expected to affect Obama's trip, the White House said, with spokesman Jay Carney saying there were "no scheduling changes to announce."

The Iran crisis is likely to take center stage, and ahead of his visit to Israel, Obama sent Vice President Joe Biden to the AIPAC conference Monday to assuage concerns among Israel's backers that the US administration was not being forceful enough with Iran.

Republican critics including Senator John McCain, who also spoke at AIPAC, have criticized the administration for appearing weak in the face of continued Iranian nuclear weapons pursuit.

But Biden was insistent that Washington was wholly committed to Israel's security.

"Let me make clear what that commitment is," a stern-faced Biden said. "It is to prevent Iran from acquiring a nuclear weapon. Period, end of discussion."

"President Barack Obama is not bluffing," Biden added, pointing at the crowd of several thousand.

"We are not looking for war. We are looking and are ready to negotiate peacefully. But all options including military force are on the table."

In addition to Iran and Syria, the moribund Israeli-Palestinian peace process will also be a topic of Obama's talks in Israel, with Netanyahu saying they would discuss efforts toward a "responsible way to advance the peace with the Palestinians."

Outgoing Israeli Defense Minister Ehud Barak, Netanyahu's representative at the AIPAC conference, on Sunday called for "a daring peace initiative vis-a-vis the Palestinians" adding that "a two-state solution is the only viable long-term solution."

The talks have stalled since late 2010, after the Palestinians insisted that all Israeli settlement building must cease.

But Barak placed the blame for the stalemate squarely on the Palestinians saying "they clearly bear most of the responsibility for past failures."