At least three Syrian opposition fighters have been killed in skirmishes in the disputed region of Nagorno-Karabakh, the Guardian has learned, confirming earlier reports of foreign involvement in the battle between Armenian and Azerbaijan over the territory and increasing fears it may spiral into a wider regional conflict. As fierce combat between Armenian and Azerbaijani forces stretched into a fourth day, the presence of Syrians on the ground – believed to be contractors working for Turkish security companies – signalled a new frontier for Ankara’s increasingly assertive foreign policy. Turkish intervention in a dispute that foreign powers have traditionally sought to restrain was a dangerous new factor that threatened to make the fighting there longer and bloodier, analysts said. It also risked drawing in other regional actors – opening a third theatre in Turkey’s power struggle with Russia, with the rivals already supporting opposite sides in conflicts in Syria and Libya, while also ringing alarm bells in neighbouring Iran. Turkey has declared its staunch support for Azerbaijan, while Russia has a military alliance with Armenia but has links and sells weapons to both sides. Turkey borders Armenia and Russia borders Azerbaijan. In Wednesday’s clashes, Armenia accused Azerbaijan of using heavily artillery across the entire front line and killing three civilians in the town of Martakert. Azerbaijan, which claims 14 of its civilians have died since Sunday, said it repelled several Armenian counter-attacks. It was not possible to independently verify either sides’ claims. Turkey and Azerbaijan have denied that Syrians are fighting in Nagorno-Karabakh and accused Armenia of deploying men from Kurdish militant groups, but have not produced proof. Several men in Syria’s last opposition stronghold of Idlib province told the Guardian this week that military commanders and brokers had offered them work guarding observation posts and oil and gas facilities in Azerbaijan on three or six month contracts at 7,000-10,000 Turkish lira (£700-£1,000) a month – relatively large sums of money which could help them escape Syria’s grinding poverty. Omar Abdo, the cousin of killed fighter Muhammed Shaalan, from the town of al Atarib, said that men in Shaalan’s unit in the al Hamza division had contacted the family on Tuesday to inform them of Shaalan’s death. “He told us he was leaving for Azerbaijan on 20 September. We don’t know the circumstances of his death and we were told it’s hard to bring his corpse at the moment, but they will try,” he said. The families of Hussein Talha, from Ain Jara village, and Sadam Aziz Azkor of al Kareem, also said unit commanders had called them on Tuesday to say that their relatives had been killed. Local media has reported another three dead. While observers have questioned why Baku’s highly-trained and well-armed military forces would be in need of assistance from Syrian mercenaries, the quick mobilisation of Syrians to the front lines, as well as the fact that Syrian volunteers said the recruitment drive began a month ago, suggested Azerbaijan had been planning its military campaign for some time. The fighting was the fiercest since a 1994 war over the region, “but it doesn’t yet look like a full-scale military offensive”, said Thomas de Waal, a senior fellow with Carnegie Europe. “So far, it’s an offensive on two or three fronts. These are small countries and they don’t want to lose men, which possibly explains shipping in these Syrians – you don’t have to sacrifice young Azerbaijani lives.” He said other powers such as Russia and Iran would be very reluctant to explicitly throw their weight behind Armenia. “Russia has its hands tied because it has relationships on both sides,” he said. “All they and Iran can do is try to get a ceasefire. Neither of them want to get involved on the ground.” While the UN and most of the international community have called for the resumption of peace talks, Turkish president Recep Tayyip Erdoğan has struck a decidedly different tone, pledging his country’s full support for Baku against what he called “Armenian aggression”. Moscow appeared to be weighing its options, urging restraint and calling for a peaceful resolution. “We call on all countries, especially our partners such as Turkey, to do everything to convince the opposing parties to cease fire and return to peacefully resolving the conflict by politico-diplomatic means,” Kremlin spokesperson Dmitry Peskov said Tuesday. The French president, Emmanuel Macron, is already at loggerheads with his Turkish counterpart in a dispute over oil and gas drilling rights in the eastern Mediterranean, and said on Wednesday: “France remains extremely concerned by the warlike messages Turkey had in the last hours, which essentially remove any of Azerbaijan’s inhibitions in reconquering Nagorno-Karabakh. And that we won’t accept.” With the deployment of Syrians, Turkey may be seeking to repeat a strategy that worked well in Libya earlier this year. Ankara has facilitated the arrival of at least 10,000 Syrians to the north African state’s battlefields, helping turn the tide of the war in favour of the UN-backed government fighting renegade General Khalifa Haftar.