ANKARA (Reuters) - Turkey is discussing with Russia and the United States a potential military offensive in a region of northeast Syria controlled by Kurdish fighters, a Turkish defense official was cited as saying by state media on Tuesday.

Turkey wants to set up a safe zone in the border area east of the Euphrates river after most U.S. troops pull out.

The American military has been supporting Kurdish-led forces there who are fighting remnants of the caliphate declared by Islamic State in Iraq and Syria in 2014. Turkey, however, views the Kurdish YPG fighters as terrorists and has repeatedly threatened to launch operations against them.

“On preparations for the east of the Euphrates, which is still on the agenda, coordination with the United States and Russia in particular continue,” defense ministry spokeswoman Nadide Sebnem Aktop said.

Aktop was also quoted by the state-owned Anadolu news agency as saying that coordination between Ankara and Moscow over the northwestern Syrian region of Idlib, where the two countries agreed to establish a de-militarized zone, continued successfully “despite provocations”.

Last week, Turkey’s Defence Minister Hulusi Akar said Russian forces would begin patrols on the border region outside Idlib and Turkish forces would start patrols inside the zone.

Turkey’s ties with Russia have caused tensions between Ankara and the United States, with Washington warning of potential U.S. sanctions if its NATO ally pushed on with a deal to purchase S-400 Russian defense systems, which are not compatible with NATO systems.

On Tuesday, Aktop said that the S-400 systems, which President Tayyip Erdogan has said Turkey would not turn back from, would be delivered in July and installed in October.

The United States has said that doing so will jeopardize Turkey’s procurement of Lockheed Martin F-35 fighter jets and other defense industry deals, including a potential deal on Raytheon Co. Patriot defense systems.

Aktop added that Turkey and Russia were also coordinating joint patrols in the region of northern Syrian town of Tel Rifaat, which is controlled by Kurdish-led forces.