Turkey said that radar used by Russian aircraft and its surface-to-air missile systems in Syria locked on to Turkish jets as the Russian air campaign intensifies against opposition targets.

The Turkish military said that eight Turkish F-16 fighters patrolling the Turkish Syrian border had been threatened by a Mig-29 and later by an anti-aircraft missile system. In both cases the threat consisted only of Russian use of radar for a limited period, but the Nato Secretary-General Jens Stoltenberg said that Russian actions were “very serious – even dangerous”. “It doesn’t look like an accident, and we’ve seen two of them over the weekend.”

Meanwhile, Russian air strikes are increasing in number against targets in territory held by Isis. The Syrian Observatory for Human Rights said that in the past 24 hours there were 34 air strikes in Palmyra which was captured by Isis on 22 May. The attacks are said to have killed 15 fighters and destroyed 10 vehicles. Air strikes against Raqqa, the Isis de facto capital in Syria, killed two fighters, while other raids took place north of Aleppo and close to Latakia.

It is still not clear how far Russian air strikes are being launched with the aid of forward air observers on the ground calling in an attacks on precisely identified targets. The US-led air campaign against Isis has been at its most effective when acting in collaboration with the Syrian Kurdish People’s Protection Units (YPG) whose commanders can give the exact co-ordinates of a target. Even so, Isis forces as a whole have not been defeated by the US air campaign, even if they have suffered heavy casualties.

Russian naval landing ship Azov sails in the Bosphorus, on its way to the Mediterranean Sea, in Istanbul, on Tuesday (Reuters)

The friction between Russia and Turkey complicates an already highly complicated situation on the Syrian-Turkish border. This is 550-miles long and about half of it is now held by the YPG, which is threatening to move west of the Euphrates River and capture the last Isis border crossing with Turkey at Jarabulus.It might also attack Isis and other Syrian opposition forces north of Aleppo and link up with a Kurdish enclave at Afrin.

A further extension of Syrian Kurdish control, particularly if aided by US air strikes, would be a blow to Ankara. It still maintains a relationship with Jabhat al-Nura, the al-Qaeda affiliate, and the hard-line Sunni Islamic group, Ahrar al-Sham, which had been advancing in Idlib and Latakia, but is coming under Russian air attack.

In pictures: Russian air strikes in Syria Show all 19 1 /19 In pictures: Russian air strikes in Syria In pictures: Russian air strikes in Syria Syrian boys cry following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Aleppo Getty In pictures: Russian air strikes in Syria Russian defense ministry spokesman Major General Igor Konashenkov speaks to the media in Moscow, Russia. Konashenkov strongly warned the United States against striking Syrian government forces and issued a thinly-veiled threat to use Russian air defense assets to protect them AP In pictures: Russian air strikes in Syria Syrians wait to receive treatment at a hospital following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Alepp Getty In pictures: Russian air strikes in Syria Russian Deputy Defense Minister Anatoly Antonov speaks at a briefing in the Defense Ministry in Moscow, Russia. Antonov said the Russian air strikes in Syria have killed about 35,000 militants, including about 2,700 residents of Russia AP In pictures: Russian air strikes in Syria Jameel Mustafa Habboush, receives oxygen from civil defence volunteers, known as the white helmets, as they rescue him from under the rubble of a building following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Aleppo Getty In pictures: Russian air strikes in Syria Civil defence members rest amidst rubble in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria Reuters In pictures: Russian air strikes in Syria A girl carrying a baby inspects damage in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria Reuters In pictures: Russian air strikes in Syria Civilians and civil defence members look for survivors at a site damaged after Russian air strikes on the Syrian rebel-held city of Idlib, Syria Reuters In pictures: Russian air strikes in Syria Civilians and civil defence members carry an injured woman on a stretcher at a site damaged after Russian air strikes on the Syrian rebel-held city of Idlib, Syria Reuters In pictures: Russian air strikes in Syria Volunteers from Syria Civil Defence, also known as the White Helmets, help civilians after Russia carried out its first airstrikes in Syria In pictures: Russian air strikes in Syria The aftermath of Russian airstrike in Talbiseh, Syria In pictures: Russian air strikes in Syria Smoke billows from buildings in Talbiseh, in Homs province, western Syria, after airstrikes by Russian warplanes AP In pictures: Russian air strikes in Syria Russian Air Forces carry out an air strike in the ISIS controlled Al-Raqqah Governorate. Russia's KAB-500s bombs completely destroy the Liwa al-Haqq command unit In pictures: Russian air strikes in Syria Caspian Flotilla of the Russian Navy firing Kalibr cruise missiles against remote Isis targets in Syria Â© TASS/ITAR-TASS Photo/Corbis In pictures: Russian air strikes in Syria Russia claimed it hit eight Isis targets, including a "terrorist HQ and co-ordination centre" that was completely destroyed In pictures: Russian air strikes in Syria A video grab taken from the footage made available on the Russian Defence Ministry's official website, purporting to show an airstrike in Syria In pictures: Russian air strikes in Syria A release from the Russian defence ministry purportedly showing targets in Syria being hit In pictures: Russian air strikes in Syria Russia launched air strikes in war-torn Syria, its first military engagement outside the former Soviet Union since the occupation of Afghanistan in 1979. Russian warplanes carried out strikes in three Syrian provinces along with regime aircraft as Putin seeks to steal US President Barack Obama's thunder by pushing a rival plan to defeat Isis militants in Syria In pictures: Russian air strikes in Syria Caspian Flotilla of the Russian Navy firing Kalibr cruise missiles against remote Isis targets in Syria, a thousand kilometres away. The targets include ammunition factories, ammunition and fuel depots, command centres, and training camps Â© TASS/ITAR-TASS Photo/Corbis

Whatever Turkey’s intentions in Syria since the start of the uprising in 2011, it was not to see the Syrian Kurds gain control of a band of territory across its southern frontier. A Turkish ground invasion into Syria, though still a possibility, would now be riskier with Russian aircraft operating in areas where Turkey would be most likely to launch an incursion.

The danger for the Turks is that they now have two Kurdish quasi-states, one in Syria and one in Iraq, immediately to the south. Worse, the Syrian-Kurdish one, known to Kurds as Rojava, is run by the Democratic Union Party (PYD) which is effectively the Syrian branch of the Kurdistan Workers Party (PKK) which has been fighting the Turkish state since 1984. Any insurgency by the PKK in Kurdish areas in south-east Turkey in future will be strengthened by the fact that the PKK has a de facto state of its own.

It appears that Turkey’s four-year attempt to overthrow President Bashar al-Assad has failed. It is unclear what Turkish President Recep Tayyip Erdogan can do about this since support from Nato is at this stage purely rhetorical. As for Turkey’s relations with Russia, Mr Erdogan says that any attack on Turkey is an attack on Nato and that “if Russia loses a friend like Turkey with whom it has co-operated on many issues, it will lose a lot.” But in Syria, at least, it appears that it is Turkey that is the loser.