A leading defense research group has distributed what it says is satellite imagery that suggests Syria may be preparing to receive Russian forces.

IHS Jane's said Tuesday that images dated a day earlier show construction of new buildings, surface clearing, the grading of terrain and the presence of tents like those used by Russian military units at the Istamo weapons storage complex and Al-Sanobar military complex north of the Syrian coastal city of Latakia.

The publication says images also showed "a substantial increase in fast jets stationed on the runway."

Russia has been one of President Bashar Assad's strongest allies. It has earlier said its recent military buildup in Syria is designed to fight the Islamic State group and President Vladimir Putin's spokesman Dmitry Peskov refused to comment further Tuesday.