JERUSALEM (Reuters) – Israel held out the possibility on Tuesday that it would not engage with U.S. President Joe Biden on strategy regarding the Iranian nuclear programme, urging tougher sanctions and a “credible military threat” against its arch-enemy.

The remarks by Israel’s envoy to Washington came at a touchy juncture for Prime Minister Benjamin Netanyahu. Up for re-election next month, he has revived his hard line on Iran while not yet having any direct communication with Biden.

The new administration has said it wants a U.S. return to a 2015 nuclear deal with Tehran – which former President Donald Trump quit, restoring sanctions – if the Iranians recommit to their own obligations. Washington has also said it wants to confer with allies in the Middle East about such moves.

“We will not be able to be part of such a process if the new administration returns to that deal,” Ambassador Gilad Erdan told Israel’s Army Radio.

Netanyahu aides have privately questioned whether engaging with U.S. counterparts might backfire, for Israel, by falsely signalling its consent for any new deal that it still opposes.

Israel was not a party to the 2015 deal. It has powerful advocates within the U.S. Congress, however, and Netanyahu’s threats to take unilateral military action on Iran if he deems diplomacy a dead end also figure into big-power planning.

“We think that if the United States returns to the same accord that it already withdrew from, all its leverage will be lost,” Erdan said.

“It would appear that only crippling sanctions – keeping the current sanctions and even adding new sanctions – combined with a credible military threat – that Iran fears – might bring Iran to real negotiations with Western countries that might ultimately produce a deal truly capable of preventing it breaking ahead (to nuclear arms).”

The Biden administration has said it wants to strengthen and lengthen constraints on Iran, which denies seeking the bomb.