ISRAEL’S next prime minister, Benjamin Netanyahu, will face an early test when he finally takes office in the next few weeks: should he ditch an election pledge and follow his defence chiefs’ strategic advice to explore a peace treaty with Syria?

During his campaign Netanyahu, the leader of the conservative Likud party, had struck a belligerent note and pledged he would never agree to Syria’s main demand that the Golan Heights, seized by Israel in the 1967 war, should be returned.

On reaching office, however, Netanyahu will be presented with reports compiled by Mossad, the overseas spy agency, and by military intelligence, that strongly advocate opening negotiations with President Bashar al-Assad of Syria.

According to sources familiar with the documents, both Amos Yadlin, the head of military intelligence, and Meir Dagan, his Mossad counterpart, recommend a deal not only to eliminate the risk of war with Syria but also to create a split between Damascus and Iran, Israel’s arch foe.

A United Nations report last week said Iran had accumulated a stockpile of more than one ton of low-enriched uranium hexafluoride at its nuclear facility in Natanz. If highly enriched this would be enough for a nuclear weapon.

Intelligence analysts say no Israeli government could accept a nuclear-armed Iran. But if it came to a showdown Israel would want Syria, which has close ties to Iran, to stay neutral. It also wants Syria to stop supplying arms to Hezbollah, the Islamic political and paramilitary group in Lebanon.

Israel has recently violated Syrian sovereignty on three occasions: with the assassination of Imad Mughniyeh, a Hezbollah leader, in Damascus last February; the killing of a Syrian general, Mohammed Suleiman, near the Syrian port of Tartous last August; and a raid on an alleged nuclear facility in September 2007.

The reports argue that Israel is vulnerable to Syria’s upgraded chemical weapons capability, which is being expanded with the help of North Korean experts. Satellite images that emerged last week showed new construction work at the heavily protected site of al-Safir.

Netanyahu, who was prime minister from 1996 to 1999, is likely to form a coalition with religious parties and the Yisrael Beiteinu (Israel is Our Home) party, led by Avigdor Lieberman, the secular rightwinger.

Yesterday Senator John Kerry, the former US Democratic presidential candidate, visited Assad amid signs that Washington is stepping up pressure on Israel to negotiate a deal.

As prime minister Netanyahu came close to signing an agreement in 1998 with Hafez al-Assad, the late Syrian president, in which he agreed to give back the Golan in return for a lasting peace.

“Indeed I did have negotiations with the Syrians,” Netanyahu admitted in an interview in 2007. “I told Assad I’d need Mount Hermon [a 4,000ft Israeli outpost overlooking Damascus] because I need radar to look towards Iran, and Assad gave up the mountain. I was surprised and happy.”

Aides close to Netanyahu say an agreement with Syria is the surest way for Netanyahu to make political progress with the new administration, as they profoundly disagree on other aspects of a Middle East peace deal.

“If he achieves a real breakthrough with Syria, he expects the Americans to give him a break with the Palestinians,” said a close aide of Netanyahu.

At least one rocket fired from Lebanon landed in northern Israel yesterday, wounding three people and prompting Israel to respond with an artillery attack.