Foreign ministers from major powers raced against the clock in the Swiss town of Lausanne Monday on the eve of a deadline to nail down the final pieces of a framework deal they hope will put any Iranian nuclear bomb out of reach.

Meanwhile in Israel, Prime Minister Benjamin Netanyahu warned Western powers that any agreement with Tehran would be seen as a reward for the country’s alleged “aggression” in Yemen.

“The agreement being formulated… sends a message that there is no price for aggression and, on the contrary, that Iran’s aggression is to be rewarded,” Netanyahu said, referring to Iranian support for Shiite Houthi rebels in Yemen.

“The moderate and responsible countries in the region, especially Israel and also many other countries, will be the first to be hurt by this agreement,” said the prime minister, who has waged a campaign against the emerging nuclear deal with Tehran, arguing that it will pave the way “to an Iranian nuclear arsenal.

“One cannot understand that when forces supported by Iran continue to conquer more ground in Yemen, in Lausanne they are closing their eyes to this aggression,” Netanyahu said. “But we are not closing our eyes and we will continue to act against every threat in every generation, certainly in this generation.”

Adding to the drama, Russian Foreign Minister Sergey Lavrov was set to leave the crunch talks with Iran in Switzerland and will only return if there is a “realistic” chance of a deal, his spokeswoman said.

Lavrov and his counterparts from the United States, China, Britain, France and Germany met with the Iranians in a lakeside Lausanne hotel on Monday for their first full session since missing a previous November deadline.

They want Iran to scale back its nuclear program to give the world ample notice of any dash to make the bomb and end a crisis that has threatened to escalate dangerously for 12 years.

The diplomatically isolated Islamic Republic denies wanting nuclear weapons and is calling for the lifting of sanctions that have strangled its lifeblood oil exports and its access to the global financial system.

The threat of new US sanctions, and domestic pressure on Iranian President Hassan Rouhani for his attempts at rapprochement with the West, all but rule out any further extension of the deadline.

A Western diplomat said Monday it was “yes or no” time, adding that the talks remained blocked on three major issues — the length of the accord; the lifting of UN sanctions; and a mechanism to ensure both sides stick to the deal.

Global powers have set a midnight Tuesday deadline to agree to the outlines of a deal that they will then try to finalize by June 30. Only then would Iran receive sanctions relief, diplomats said.

German Foreign Minister Frank-Walter Steinmeier said that after 18 months of negotiations, they were in the “endgame.”

Iran’s lead negotiator Abbas Araqchi said they were in the “final phase.”

But Araqchi also said the talks were “very difficult,” while Steinmeier cautioned that the “final meters are the most difficult.”

Even before a deal is sewn up, opponents have been lining up to criticize it, worrying it will not do enough to stop Iran getting the bomb.

“I just don’t understand why we would sign an agreement with a group of people who in my opinion have no intention of keeping their word,” US House Speaker John Boehner told CNN.

Israel is widely believed to be the sole, if undeclared, nuclear-armed power in the Middle East and has long been opposed to any Iran accord.

Saudi Arabia — leading an Arab coalition, which on Monday carried out a fifth straight night of airstrikes on Iran-backed rebels in Yemen — is also uneasy about any US-Iran thawing of ties.

Western diplomats say some areas in a highly complex jigsaw puzzle of an accord are tentatively agreed upon. But they caution there is a long way to go.

One said Sunday that Iran had “more or less” agreed to slash the number of its centrifuge enrichment machines from 20,000 to 6,000 and to ship abroad most of its stockpile of low-enriched uranium.

This would make it a much more lengthy process to further purify these stocks to weapons-grade.

Iranian officials dismissed the numbers as “speculation,” with Araqchi ruling out sending the stocks abroad, although he said “other options” were being examined.

This could include diluting low-enriched uranium or converting it to another form.

But, nevertheless, Iranian officials have expressed guarded optimism that a breakthrough may be at hand.

“Getting to an accord is doable. Solutions have been found for numerous questions. We are still working on two or three issues,” Araqchi said.

In addition to scaling down its nuclear program, the powers want Iran’s remaining facilities to be subject to an unprecedented level of inspections by the UN atomic watchdog.

Its underground facility at Fordo would also likely be barred from uranium enrichment, diplomats said, although it might be kept open for research purposes.

The US, EU and others are only prepared to suspend their sanctions, not terminate them, and in a phased manner in order to ensure that Iran does not violate the deal.

The issue of UN Security Council sanctions is particularly tricky.

Araqchi said Sunday there must be a “precise framework” for lifting sanctions. The duration of any deal — the US wants at least 10 and possibly up to 15 years — is also a point of contention.