<p>Turkey on Friday vowed there would be no "step back" from Ankara's controversial purchase of the Russian S-400 missile defence system despite the threat of US sanctions.</p>.<p>"There is no question of a step backwards, Turkey will activate the S-400," promised President Recep Tayyip Erdogan's spokesman, Ibrahim Kalin, in an interview with state broadcaster TRT Haber.</p>.<p>Ankara's deal with Russia and the subsequent delivery of the system in July has been a major source of tension between NATO allies Turkey and the United States.</p>.<p>Last month the US said Turkey would be spared sanctions under a 2017 law if the S-400 system is not turned on.</p>.<p>The American act, known as CAATSA, mandates sanctions for any "significant" purchases of weapons from Russia.</p>.<p>Turkey was also removed from the F-35 fighter jet programme as a consequence of the purchase.</p>.<p>The issue was on the agenda during Erdogan's talks with US President Donald Trump on Wednesday.</p>.<p>Trump told reporters after their meeting that Turkey's acquisition created "serious challenges" for Washington as he said officials would "immediately" get to work on resolving the issue.</p>.<p>Kalin said the "joint mechanism" to address the tensions over the F-35 programme and S-400s had begun on Friday.</p>.<p>As relations between Ankara and Moscow strengthen, Kalin added that Russian President Vladimir Putin planned to visit Turkey in the first week of January 2020.</p>.<p>Among the issues on the agenda during the visit will be Syria after Russia and Turkey agreed last month on the withdrawal of a Syrian Kurdish militia from the war-torn country's north following Erdogan's Russia trip.</p>.<p>Russia and Turkey have worked closely together on Syria despite being on opposing sides of the conflict as Moscow supports Damascus and Ankara has called for Syrian President Bashar al-Assad's ouster.</p>.<p>There have already been joint Russian and Turkish military patrols but Kalin said the People's Protection Units (YPG) militia had not been completely removed from Kobane.</p>.<p>"There have been some figures given regarding the terrorists' withdrawal but we have not confirmed this," Kalin told TRT.</p>.<p>Ankara says the YPG, which spearheaded the fight against the Islamic State extremist group, is a "terrorist" offshoot of Kurdish insurgents fighting against the Turkish state since 1984.</p>
<p>Turkey on Friday vowed there would be no "step back" from Ankara's controversial purchase of the Russian S-400 missile defence system despite the threat of US sanctions.</p>.<p>"There is no question of a step backwards, Turkey will activate the S-400," promised President Recep Tayyip Erdogan's spokesman, Ibrahim Kalin, in an interview with state broadcaster TRT Haber.</p>.<p>Ankara's deal with Russia and the subsequent delivery of the system in July has been a major source of tension between NATO allies Turkey and the United States.</p>.<p>Last month the US said Turkey would be spared sanctions under a 2017 law if the S-400 system is not turned on.</p>.<p>The American act, known as CAATSA, mandates sanctions for any "significant" purchases of weapons from Russia.</p>.<p>Turkey was also removed from the F-35 fighter jet programme as a consequence of the purchase.</p>.<p>The issue was on the agenda during Erdogan's talks with US President Donald Trump on Wednesday.</p>.<p>Trump told reporters after their meeting that Turkey's acquisition created "serious challenges" for Washington as he said officials would "immediately" get to work on resolving the issue.</p>.<p>Kalin said the "joint mechanism" to address the tensions over the F-35 programme and S-400s had begun on Friday.</p>.<p>As relations between Ankara and Moscow strengthen, Kalin added that Russian President Vladimir Putin planned to visit Turkey in the first week of January 2020.</p>.<p>Among the issues on the agenda during the visit will be Syria after Russia and Turkey agreed last month on the withdrawal of a Syrian Kurdish militia from the war-torn country's north following Erdogan's Russia trip.</p>.<p>Russia and Turkey have worked closely together on Syria despite being on opposing sides of the conflict as Moscow supports Damascus and Ankara has called for Syrian President Bashar al-Assad's ouster.</p>.<p>There have already been joint Russian and Turkish military patrols but Kalin said the People's Protection Units (YPG) militia had not been completely removed from Kobane.</p>.<p>"There have been some figures given regarding the terrorists' withdrawal but we have not confirmed this," Kalin told TRT.</p>.<p>Ankara says the YPG, which spearheaded the fight against the Islamic State extremist group, is a "terrorist" offshoot of Kurdish insurgents fighting against the Turkish state since 1984.</p>