WASHINGTON, Sept. 14 (Xinhua) -- The Pentagon said Monday Russia's recent military buildup in Syria indicated that it intended to create a military base in Syria.

"We have seen indications in recent days that Russia has moved people and things into the area around Latakia (Syria's coastal province) and the air base there that suggests that it intends to establish some sort of a forward air operating base," Pentagon spokesman Jeff Davis said at the daily briefing.

Davis said the Pentagon was closely monitoring the buildup, but declined to provide further details regarding the Russian military personnel and equipment being flown to Syria.

While calling Russia's military support to the Syrian government "unhelpful and risk," Davis declined to comment on whether the U.S.-led coalition had invited Russia to join the air campaign against the Islamic State (IS).

"We have said before that we would welcome Russian contributions to the overall global effort against (the IS)," he said.

The New York Times reported Monday at least seven giant Russian Condor transport planes had taken off from Russia during the past week to Syria and passed through Iranian and Iraqi airspace, citing U.S. officials who spoke on condition of anonymity.

Under the U.S. pressure, Bulgaria, a NATO member, had already closed its airspace to the Russian planes.

However, the Iraqi government had so far yet to take actions and still kept the airspace open to Russian planes despite being urged by U.S. diplomats to follow Bulgaria's example earlier this month.