A VIDEO aired on May 12th shows the 13th Brigade, a rebel group in northern Syria, destroying a government tank with an armour-piercing missile known as a TOW. Dozens of these weapons, supplied across the country under a beefed-up Saudi-American plan, are said now to be in the hands of nine groups friendly to the West.

They have helped to stem recent advances by government forces into parts of two northern provinces, Aleppo and Idleb. On May 8th rebels tunnelled under and blew up Aleppo’s Carlton Hotel, a base for President Bashar Assad’s troops; they have cut nearby government supply routes. The rebels have also gained ground in the south, on the Hauran plain close to Jordan.

Yet TOWs alone will not stop the balance of power tilting in favour of Mr Assad, who is campaigning for re-election next month. On May 8th the last 900-odd fighters were escorted across rebel lines out of Homs under a deal brokered by Iran and overseen by the UN, ending a two-year siege that has left swathes of Syria’s third-largest city in ruins. And though the extremist rebel group, the Islamic State of Iraq and Greater Syria (ISIS), has been forced back to the east of the country as a result of discord with other rebel groups, it has been at the expense of the regime recapturing parts of Aleppo taken by the rebels two years ago.

Mr Assad’s recent gains and continued brutal tactics are rattling the opposition and its backers. On May 13th Lakhdar Brahimi, who has sought to mediate on behalf of the UN and the Arab League, left his post in frustration. Ahmed Jarba, head of the Syrian Coalition, the main opposition in exile, has been in Washington asking for shoulder-fired anti-aircraft missiles as well as for more anti-tank weapons. Long denied anti-aircraft weapons lest they end up in the hands of jihadists or are used against Americans, the request has become more urgent as Mr Assad’s air force indiscriminately bombs civilians in rebel-held areas.

American officials, notably Samantha Power, ambassador to the UN, are particularly disturbed by the regime’s incessant use of barrel-bombs, crude devices packed with explosives dropped from the air, sometimes onto schools and blocks of flats. Aleppo has been grievously bashed by them of late. Mr Assad has exploited last year’s deal to hand over his chemical weapons to avert threatened American air strikes. “One of the unintended consequences of the chemical-weapons agreement was Assad’s belief that he was free to do anything he wanted to do to vulnerable civilians so long as he did it without chemicals,” says Fred Hof, a former State Department man at the Atlantic Council, a think-tank in Washington.

Even that condition appears to have been flouted. Human Rights Watch, a New York-based lobby group, notes “strong evidence” that the regime assaulted three towns in April by dropping barrel-bombs with chlorine inside them. French officials have counted 14 chemical attacks since late 2013. That is in addition to over 150,000 Syrians killed and nearly half of Syria’s pre-war population of 23m displaced.

Thanks largely to his Russian and Iranian friends, Mr Assad looks set to stay for quite a while. The rebels no longer talk of capturing Damascus soon. A survey of 250 former rebel fighters by some Harvard academics found that more than half of those who have left did so because they no longer thought the opposition could win militarily. Mr Assad probably reckons he can consolidate his control over the western portion of the country, the most heavily populated bit, and leave lawless swathes in the east and north to an increasingly unsavoury insurgency that can be worn down over time.

Though ISIS has been pushed back by rival rebels to an area around Deir ez-Zor in the east, next to their stronghold in neighbouring Iraq, it refuses to heed Ayman al-Zawahiri, al-Qaeda’s head, who has told it to leave Syria altogether. Meanwhile, Jabhat al-Nusra, al-Qaeda’s recognised affiliate in Syria, has strengthened in the south, kidnapping Ahmad Naameh, a moderate rebel leader close to the Jordanians.

Jordan and Israel are nervous. This week the Israelis closed the border with Syria traversed by UN people in the Golan Heights, which Israel has long occupied. Reports have surfaced that Jordanian officials may be co-ordinating with the authorities in Damascus to keep rebel jihadists at bay.

“Helping the legitimate opposition is the best way—and after three years we know who they are,” says Turki al-Faisal, a former Saudi intelligence chief who now runs the King Faisal Centre for Research and Islamic Studies, a think-tank in Riyadh, the Saudi capital. “Alas, even our allies have not come round to that idea.” Mr Hof reckons that handing a limited number of anti-aircraft missiles to vetted individuals could at least help to stem the bloodshed. “The first time a regime helicopter or fighter-jet is taken down, the word will go around the regime’s combat-aviation corps that the free ride killing children in their schools is over,” he says.

Hitherto people in the Pentagon have been warier than those in the State Department about arming the rebels. Moreover, as the help sent so far has been covert, it has necessarily been limited in quantity. Some in the Pentagon may be changing their mind. Yet Mr Obama is unlikely to give anything more than a handful of anti-tank weapons, at least for the time being, despite the opposition’s claim that the TOW deliveries have proved their ability to direct lethal arms to the right groups. Mr Jarba’s influence on the ground may thus weaken. On May 12th a leader of Jabhat al-Nusra accused him of embezzling $75m meant for the Syrian people.