"If they are there to shore up Assad and to certainly provide Assad with the continued sense he doesn't have to negotiate, then I think it's a problem for Syria, and it's a problem for everybody who wants to bring an end to this conflict, which has gone on for too long," Kerry said, according to Ukraine Today.

Satellite images released this week showed a build up of Russian fighter jets, tanks and helicopters at Syria's Latakia airbase. Around 500 Russian troops, reportedly including dozens of troops who had been fighting in Ukraine are camped at the base. Thousands of reinforcements are reportedly on their way.

Meanwhile, the exodus of Syrian refugees into Europe has added urgency to finding a political settlement to the Syrian conflict.

See unian.info’s video section for more of the latest news from Ukraine in video from Ukraine Today, Ukraine’s 24-hour English-language news channel.