Faced with "faster and faster" centrifuges spinning in Iran, Israeli Prime Minister Benjamin Netanyahu warned Monday that Tehran's nuclear program was getting closer to crossing a crucial "red line."

Speaking via satellite link from Jerusalem to an influential pro-Israel lobby group, the remarks reiterated Netanyahu's apparent impatience with the policy of leading nations to use sanctions to suppress Iran's atomic ambitions.

Instead, the comments seemed to underscore Netanyahu's desire to see Tehran face a more robust military threat, in the wake of talks last week between the world's top powers and Iranian negotiators on the disputed nuclear program.

"Iran enriches more and more uranium, it installs faster and faster centrifuges," Netanyahu told the American Israel Public Affairs Committee (AIPAC), the largest pro-Israel lobby in the United States.

"We have to stop its nuclear enrichment program before it's too late," he said, asserting that Iran is "running out the clock" on the international community's efforts to prevent the country from obtaining an atomic weapon.

The Israeli prime minister warned that leaders in Tehran had opted to "just grit their teeth" through punishing international sanctions and pursue their plans, 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 arch foe 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."

Last week's talks in Almaty saw the UN Security Council's five permanent members -- Britain, China, France, Russia, and the United States -- and Germany offer Iran a softening of non-oil or financial sector-related sanctions.

In return, the P5+1 powers asked Iran for concessions over its sensitive uranium enrichment operations.

A senior US official said Iran "appeared to listen carefully to the offer" and its chief negotiator Saeed Jalili issued rare praise for the world powers, noting that the Almaty meeting may later be viewed as "a milestone."

However, ahead of his talks with US President Barack Obama later this month, Netanyahu stressed that Iran's leaders have "used negotiations, including the most recent ones, to buy time to press ahead with its nuclear program."

There must be "a clear and credible military threat if diplomacy and sanctions fail," the Israeli leader said.

Netanyahu won re-election earlier this year but has so far struggled to stitch together a coalition. 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 Obama on an official visit -- his first as US commander in chief.

The two leaders would discuss Iran as well as Syria, where a civil war is raging nearly two years after the start of an uprising against President 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.

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 as closely allied with Israel as previous presidents.

"Israel's legitimacy and our support for it is not a matter of debate. There is no light" between the two countries, Biden insisted.

Republican critics including Senator John McCain, who also spoke at AIPAC, have criticized the administration for appearing weak on Iran.

"The latest efforts at conciliation... have failed," McCain said, referring to last week's talks in Kazakhstan.

"It's very clear they are on the path to having a nuclear weapon," McCain said of Iran. "I don't think it's a question of whether, it's obviously a question of when."

But a stern-faced Biden was insistent that Washington's aim was "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.

Earlier, US Secretary of State John Kerry said after talks with officials in Gulf states that the P5+1's discussions with Iran "cannot become an instrument for delay that in the end makes the situation more dangerous."

"There is a finite amount of time," he added.