"We won’t speculate on the comments of President Assad. But as the NATO Secretary General has repeatedly said, the substantial military build-up of Russian forces in Syria and the Eastern Mediterranean has further complicated this conflict," the NATO official said.
NATO's comment on the "substantial military build-up" comes amid the March decision by Russian President Vladimir Putin to pull out the bulk of the Russian contingent in Syria as the campaign's objectives had broadly been achieved.
The NATO official also added that Russia should "contribute to de-escalating the crisis in Syria" and not "prolonging it."
Following Putin’s announcement of the withdrawal, Moscow said that some Russian military personnel would remain at the Hmeimim air base as well as the naval base at Tartus to observe the implementation of the ceasefire in Syria.