Kremlin aide Yuri Ushakov said on Monday that Russia wanted Turkey to ensure its military incursion into northern Syria was proportionate with the situation.

Ushakov, speaking in Riyadh during an official visit to Saudi Arabia by President Vladimir Putin, was commenting on Turkey's military operation which it launched last week.

Ushakov said the main thing for Moscow was that Turkey's offensive - which targets Syrian Kurdish militia seen by Ankara as aligned with Kurdish separatists in Turkey - not harm efforts to find a political solution to Syria's eight-year-old war.

Around the time when Ushakov made his comments, Turkey's Defence Ministry tweeted that Defence Minister Hulusi Akar and his Russian counterpart Sergei Shoigu had discussed Syria and issues of security and defence in a phone call.

On Monday, Russian-backed Syrian government forces wasted no time in taking advantage of an abrupt U.S. retreat from Syria after the Turkish incursion, deploying deep inside Kurdish-held territory south of the Turkish frontier.