Russia has kept a considerable military presence in conflict-torn Syria to bolster the Damascus government, NATO chief Jens Stoltenberg said Thursday.

Russia has kept a considerable military presence in conflict-torn Syria to bolster the Damascus government, NATO chief Jens Stoltenberg said Thursday.

"Despite the announced partial withdrawal we see that Russia maintains a considerable military presence in support of the (President Bashar) Assad regime in Syria," he said at a press conference in Turkey.

A month ago Russian President Vladimir Putin surprised the West by ordering the main part of his forces to pull out.

Despite Moscow having signed on to efforts to promote a political settlement in Syria, it stressd that the ceasefire agreed with the US does not include Takfiri terrorists like ISIL and Nusra Front.

Since the Kremlin said it was scaling down its air presence in the country, the Syria forces -- backed up crucially by Russian firepower -- have scored some of their most dramatic successes in areas not covered by a February ceasefire.

The landmark partial ceasefire, which was negotiated by the US and Russia, had dramatically curtailed violence across much of Syria and raised hopes that a lasting deal could be struck to end the bloodshed.

Stoltenberg said the Syrian ceasefire "is under strain" but "remains the best basis for a negotiated peaceful solution to the crisis".