Lebanon was grappling to maintain its fragile peace today as Syrian fighter jets fired rockets into its territory in what appeared to be an act of admonition from Damascus as it demands a clampdown on militants and arms crossing the border.

The salvo of four regime rockets – which struck around 5km from the border – caused no casualties but sparked panic in the nearby border town of Arsal, home to thousands of refugees in addition to rebel fighters and weapons smugglers. The attack came as Syria’s opposition National Coalition met in Istanbul to attempt to form a new transitional government – though some parties on the ground remain skeptical of what many see as an external organisation.

As the two-year civil war marches on next door, Lebanon is facing an escalating array of threats to its stability, struggling with sectarian clashes, strikes and the burden of hundreds of thousands of refugees. Protesters blocked roads in Beirut for a second day today after four Sunni sheikhs were attacked in two incidents over the weekend.

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The strikes near the border were only the second time Syrian planes have struck Lebanon since the conflict began. Damascus threatened just three days ago to strike targets in Lebanon if the government did not improve border security, saying it was practicing “self restraint” by not hitting gatherings of “armed gangs”.

“People are scared,” said Wafic Khalaf, a member of Arsal’s municipal council. “It’s a warning.”

In Istanbul, National Coalition’s 73 members are expected to vote on a prime minister tomorrow before moving the interim government into rebel held areas in the north of the country in the coming weeks.

Most of the ten candidates for prime minister announced by the coalition are technocrats and businessmen based abroad, making it uncertain whether they will be able to garner legitimacy if and when they move into northern Syria. The names of two other candidates within Syria were not released for security reasons. The frontrunners are understood to be Ghassan Hitto, an IT executive from Dallas; Osama Kadi, an economist from Ontario, and Asaad Mustapha, a former agriculture minister.

General Salim Idris, head of the Western-backed Supreme Military Council, came out in support of the initiative and said his men would protect members. “We recognise the coalition as our political umbrella and we hope this government can be formed unanimously and that this government will exercise its powers in all of Syria,” he said. “We consider it the only legal government in the country.”

However, it is unclear how much of the disparate Free Syrian Army he speaks for. “The fighters will not recognise any government except one that’s from the inside, that has fought beside them,” said one rebel with the Ansar al Deen battalion. “Maybe they will get some recognition from the West or outside, but not from us.”

The opposition coalition has appealed for international support, while it pushes for greater military assistance. US Secretary of State John Kerry today said his government would not stand in the way of British and French efforts to arm the rebels as they lobby for the end to the EU arms embargo against the country.