While international focus is on the devastating bombing going on in Aleppo, another offensive is taking place, much of it in the shadows, which could be a game-changer in Syria's bloody civil war.

 

The Turkish military, with armour, air-power and troops on the ground - a thousand of them special forces - are moving deeper into Syria, along with Syrian opposition fighters, setting up a "security zone" across the border.

 

Operation Euphrates Shield has been marked for Ankara by increasing acrimony with Washington and warming of relations with Moscow. The Turkish forces have attacked Kurdish fighters who are America's key allies in the fight against Isis, while Russia, busy securing Aleppo for ally Syrian President Bashar al-Assad, has given tacit approval for President Recep Tayyip Erdogan's actions in northern Syria.

 

Washington's warning to Ankara against striking the Kurdish People's Protection Units (YPG) and the Syrian Democratic Forces (SDF) which claims to be an alliance of Syrian Arabs and Kurds, have been ignored. Now Turkish forces are said to be poised outside the town of Manbij alongside the Free Syrian Army (FSA) to drive out the SDF who took it from Isis. There is even talk among senior Turkish officials of crossing the Euphrates river - which the Americans consider to be the boundary of Kurdish influence - to "deal with" its Kurdish enemies.

 

The prospect of these violent clashes comes as the time approaches for the final offensive against Isis, the Islamist terrorist group they are all supposed to be fighting, and the drive to take Raqqa, the "capital" of Isis.

 

President Erdogan said earlier this week: "Of course, if the United States wants to do the Raqqa operation with the YPG and the Democratic Union Party [PYD - a Kurdish organisation] we as Turkey will not take part in this operation; but if they exclude the YPG and PYD from this affair, then of course we will conjoin this struggle together with the United States".

 

Mr Erdogan has continued to condemn the US for supporting the Kurds, saying "if you think you can finish off Daesh [Isis] with the YPG and PYD then you cannot do so. Three days ago America dropped two plane loads of weapons in Kobani for these terrorist groups." He had, he added, complained about this to US Vice President Joe Biden.

 

But the US continues to see the YPG and SDF as an essential part of the campaign against Isis and this has been the message delivered to the Turks at recent meetings in Ankara. Hillary Clinton, who appears likely to be in the White House after the US elections, despite Donald Trump's unexpectedly strong showing in the polls, stressed during this week's presidential debate that America must "support our Arab and Kurdish partners to be able to actually take out Isis in Raqqa".

 

Asked whether arming the Kurdish fighters would bring success against Isis, the chairman of the US military's Joint Chiefs of Staff, General Joseph Dunford, said: "I would agree with that, if we reinforce the SDF's current capabilities, that will increase the prospects of our success in Raqqa."

 

It is not just Syria which has been a bone of contention with America. Mr Erdogan and his colleagues are extremely critical of Washington for failing to hand over the Pennsylvania-based cleric, Fethullah Gulen, who they accuse of plotting the attempted coup two months ago. The US administration says the matter is going through due judicial process, but some officials in Washington have privately expressed doubts that the evidence presented so far by Ankara justifies extradition. Mr Gulen denies taking any part in the coup.

 

While Ankara's relation with the US has worsened, there has been a significant thaw in relations with Moscow since Turkish jets shot down a Russian plane in November. After a period of confrontation during which a furious Vladimir Putin imposed trade sanctions, President Erdogan climbed down, expressing his regrets over what happened. Talks have been held since then and the Turkish leader was called a "dear friend" by President Putin during a visit to St Petersburg last month.

 

The rapprochement has continued over Turkey's Syria incursion. Talha Kose, an academic and senior member of a think tank, SETA, which was founded by President Erdogan's spokesman Ibrahim Kalin, said: "The Russians are not objecting to what Turkey is doing in northern Syria. This is partly because they are really focusing on Aleppo now, but also what Turkey is doing is not harming their interests. Turkey sees what America is doing in Syria as harming Turkish interests."

 

Merve Tahiroglu, an analyst at the Foundation for the Defence of Democracies, said: "Turkey, embittered by Washington's close cooperation with the YPG will act increasingly independent from the US in Syria. The picture is getting complicated and much will depend on the new Moscow-Ankara hotline".

 

This action, independent from the US, is going to include the attempt to set up a "safety zone" inside Syria, something Ankara had long wanted and US and the West have steadfastly opposed. Mr Erdogan said: "As part of the Euphrates Shield operation, an area of 900 square kilometres has been cleared of terror so far. This area is pushing south. We may extend this area to 5,000 square kilometres as part of a safe zone."

 

Turkish forces and FSA units took the city of Jarablus after Isis forces withdrew. As well as helping towards establishing a "safety zone", the move stopped the Kurds from acquiring another link for their chain of cantons - a plan, claim the Turks, to create a Kurdish state which will try to incorporate Kurdish territories in Turkey.

 

Turkey's President has also indicated that the next target for his forces and those of the FSA would be Isis-held al-Bab. The US Defence Secretary, Ashton Carter, has stressed that Washington does not want to see Turkish forces or the FSA in the city. The YPG is also trying to get there and, in Ankara's eyes, this is more proof of American support for the Kurds.

 

Al-Bab is a city of tremendous strategic and symbolic significance. It was one of the first places in northern Syria to rise up against the Assad regime and was subsequently occupied by Jabhat al-Nusra, an al-Qaeda affiliate, and then Isis.

 

The name al-Bab means "The Gate" and it is seen as a key route into the heart of the Isis "Caliphate". The race to be the gatekeeper there will have great significance not just for the war against Isis, but Turkey's relations with the US and the West.