Saleh Muslim, the leader of the main Kurdish political party in Syria, the PYD, confirmed that 50 tons of ammunition were dropped to the Kurdish fighters and their allies.

“This is just the beginning, more weapons are to be sent,” he told the Firat news agency, which is affiliated with Kurdish militants in Turkey and Syria.

The US has not confirmed exactly for whom it delivered military assistance, but said only that the small arms ammunition went to Syrian Arab groups vetted by Washington.

“This seeks to build on some of the successes that those forces have had in clearing Syrian territory and is supported by coalition airstrikes,” Mark Toner, a State Department spokesperson, said.

The Kurdish YPG fighters have been the most effective force on the ground pushing back the Islamic State extremists and have received regular help from US-led airstrikes.

The YPG recently announced the formation of a wider coalition with some Arab militias, though analysts have indicated the Kurds remain the main force in the new grouping.

There have been signs from within Syria that the Kurdish forces and their allies may soon push on the Islamic State’s de-facto capital in Raqqa city.

A commander of a mostly-Arab battalion close to the YPG told the website Syria Direct they had already received weapons, but did not specify their source.

“We have received promises surrounding future military aid and we really did begin to receive equipment to exterminate [Islamic State] in Raqqa city and its countryside,” the commander said, using a pseudonym.

Wrong hands 

The main concern for Turkey is that the YPG in Syria is fuelling nationalist sentiments among its own Kurdish minority and that weapons sent to the neighbour could end up in the hands of the armed Kurdistan Workers’ Party (PKK).

The PKK, which has been in conflict with the Turkish state since 1984, is closely linked to the YPG.

“We will not hesitate even a moment, if the weapons aid to PYD so close to Turkish border becomes a threat to Turkey in any way,” Davutoglu said, warning Turkey could take action.

Turkey’s unease comes as it sees rebels fighting President Bashar Assad on the back foot, with Russia’s intervention last month to help the government forces.

Turkey has long been a supporter of rebel factions, including some hardline Islamic groups that Western nations have rejected as partners.

“The Russian intervention hurts Turkey’s efforts because it bolsters Assad,” said Aaron Stein, a researcher at the Atlantic Council, noting that Moscow stepped in after Assad, its main Arab Middle Eastern ally, was faltering.

While Russia, which has its only Mediterranean Sea naval post in western Syria, initially said it was launching airstrikes to target the Islamic State, most of its bombardments, including artillery fire, has been aimed at rebels.

“Russia is trying to make a massive step towards supporting the Assad regime,” said Hasan Selim Ozertem, researcher at the Ankara-based think tank the International Strategic Research Organisation.

Assad’s forces, which for months had been under pressure and facing losses, are now in the advance. They are poised to take a strategic section of Homs province from the opposition.

Red line 

For now, Turkey’s red line would appear to be any weapons ending up in the hands of the PKK – especially after a ceasefire with the group collapsed in July, leading to renewed conflict inside Turkey, leaving hundreds dead.

Also, Turkey would not tolerate Syrian Kurds crossing westward across the Euphrates River to take fresh territory in north Syria, in a zone currently held by Islamic State. Turkey wants rebel factions to gain this area along its border.

But this all points to the likelihood that Syria will, for the foreseeable future, fail to become a unitary state, even though this is against the stated interests of some of the major powers involved, especially Turkey.

There are several key developments: Russia’s intervention to secure territory for the government; Turkey’s insistence on who can control which swathes of land in the north; Saudi Arabia’s backing of a rebel southern front near Jordan; and the Iranian support for the Shi’ite Hezbollah movement along the Lebanese border.

“Syria is de facto being divided up along the interests of regional and international powers involved,” says Stein.