The US and Russia are working to establish air bases in Northern Syria, within 30 miles of each other, an activist group has claimed. Russian warplanes are expected to begin using the Qamishli International Airport, according to the British-based Syrian Observatory for Human Rights.
The base needs fortification, but teams of Russian experts had arrived to "explore its readiness and to check what is needed to develop and use it", the Observatory said. The activist did not say when the base, which is currently controlled by forces loyal to Syrian President Bashar Assad, would be operational.
Turkey's president Recep Erdoğan said his country "would not tolerate such formations" within a few miles of his country's border. "We maintain our sensitivities on these issues," he said, adding that he would discuss the matter in a meeting with US Vice President Joe Biden at a 23 January meeting.
Reinforcements were later sent to the country's border, where soldiers began digging trenches.
Tensions between the two countries have been high since Turkey shot down a Russian Su-24 warplane on its border with Syria on 24 November.
Less than 30 miles away from the Russian base, US special operations troops have reportedly taken over the Rmeilan Airbase, near Syria's Iraqi and Turkish borders.
American helicopters have operated out of the base, according to the Observatory which claims that sources on the ground have told them that work to expand the runway has been taking place over recent weeks.
It is expected to be the start point for US airstrikes against Islamic State (Isis), they added.
The airfield was until recently under the control of Syrian Kurdish forces, known as the YPG but was turned over to the Americans to help expand support for the Syrian Democratic Forces (SDF), an SDF spokesperson Taj Kordsh, told Al-Jazeera.
However, the claims were denied by US Air Force Colonel Patrick Ryder who said the US military had "not taken control of any airfields in Syria".
"Our location and our troop strength remain small," he said. "That being said, US forces in Syria are consistently looking for ways to increase efficiency for logistics and personnel recovery support." He added: "The reporting that you've seen related to that, is incorrect. There's been no change to the size or mission of the US presence in Syria."