Amateur video obtained from social media purports to show the aftermath of air raids over the Syrian town of Ras al-Ain Reuters

The Syrian opposition says it has been promised western military support in return for forming a united front, in advance of a donors' conference in London on Friday intended to consolidate the new rebel coalition.

British diplomats said Friday's expert-level meeting would discuss purely non-lethal aid to the National Coalition of Syrian Revolutionary and Opposition Forces, formed on Sunday in Doha, but neither the UK nor French governments are ruling out arming the opposition in the coming months in an attempt to break the bloody deadlock in Syria.

The conflict showed more signs of spreading as Israeli tanks fired at Syrian positions for the second time in as many days in response to Syria mortar fire landing on the Israeli-held Golan Heights, and a Syrian government jet bombed a rebel-held village just yards from the Turkish border.

Turkey has raised the possibility of asking Nato to deploy Patriot anti-aircraft missiles along its southern border. It has yet to put a formal request to the alliance, but Turkish officials said the latest bombing showed it was necessary for it to strengthen the defences on its southern flank. Turkey, which has about 120,000 Syrian refugees on its territory, is also pushing for expanding western backing for the rebels.

The new National Coalition, which claims to represent 90% of Syrian opposition groups, including the various rebel armed forces inside the country, won recognition from Gulf states night but looked likely to win only observer status at Tuesday's Arab League meeting in Cairo.

It hopes to be recognised as the legitimate representative of the Syrian people by western nations at a meeting of the Friends of Syria in Marrakech next month.

"The international community realises the situation in Syria is unsustainable and that its own self-interest is at stake as it destabilises the region," said Yaser Tabbara, a coalition spokesman. "We have assuaged a lot of the concerns and fulfilled a lot of preconditions on the Syrian armed opposition in terms of accountability and unity, and I believe the international community is ready to invest in the opposition both militarily and politically. That is the sense we got in Doha."

Tabbara said the coalition would be asking for "the types of weapons with which we can enforce our own no-fly zones", a reference to portable anti-aircraft missiles which the rebels have long been seeking. Western officials have had deep misgivings about providing such missiles in case they ended up in terrorist hands and used against civilian airliners, but they are increasingly alarmed about the destabilising consequences of non-intervention. Qatar and Saudia Arabia have provided most of the rebels' arms supplies, but those weapons have gone disproportionately to extremist Salafist and jihadist groups, who have been increasingly prominent in Aleppo and other fronts in the civil war.

Britain and the US are reviewing their policy of restricting their assistance to non-military equipment. Prime minister David Cameron is frustrated with the military impasse and the rising death toll, so the British government has announced it is opening talks with rebel commanders. The French military are believed to be making contingency plans for supplying weapons. Welcoming the formation of the National Coalition, the French foreign minister, Laurent Fabius, made a pointed reference to the prospect of arming the opposition.

"France – who recognizes the Syrian people's right to defend themselves against the attacks of the criminal regime in Damascus – very much hopes this coalition can be quickly consolidated, enjoying the broadest possible support from Syrians and the international community," Fabius said.

Western officials have been urging the coalition leadership to act fast to turn the Doha agreement into an functioning alternative administration, to speed international recognition and arms supplies. "We are not entirely there," a European diplomat said.

Syrian opposition leaders say, in return, they can only establish the necessary structures once they receive more western backing.

"We keep hearing about this concept of sequencing,"

Tabbara said. "But we are in a Catch 22. We are told we will get the serious support once we have operational structures in place but we in the middle know things are more complex. In order to build a government with full authority inside the country, we need support and political recognition. We are trying to balance this Catch 22 as delicately as we can, and try to move in parallel with the demands of the international community."

Syria is likely to figure in the EU summit next month, but so far no member state has put the existing EU arms embargo on the agenda. Revising or lifting it would require the unanimous agreement of all 27 member states. British lawyers are looking at whether the wording of the embargo agreement, allowing a state to supply weapons if it determines it "is intended solely for humanitarian or protective use", provides a loophole.

Western capitals may hope that the credible threat of heightened intervention could be enough to persuade Russia and China to agree to a UN security council resolution putting sanctions on President Bashar al-Assad.

Russia has thus far been adamantly opposed to a punitive UN action against the regime, a close regional ally. Russia gave the new coalition a cool reception, urging it to negotiate with Assad and to reject "outside interference".