Russia has deployed additional troops to two new bases in Syria amid growing concerns about Moscow's real purpose since the Russian incursion was apparently not coordinated with other countries operating in the war-torn country, CNN reported.

President Vladimir Putin initially set up an airbase and sent tanks, artillery and fighters to Syria—a move that stunned many Western leaders given that the Russian strategy appears in sharp contrast to US President Barack Obama's approach of an air campaign over Syria but less military action on the ground in that country.

Citing a research firm, CNN said two previously unreported sites have been spotted in satellite imagery of western Syria "where steps appear to be taken to receive Russian forces."

The two new sites are the Istamo weapons storage complex and the Al-Sanobar military complex, both north of the Latakia base, analysts of IHS Jane said.

"Military personnel would likely arrive at these two bases as part of the rapid expeditionary force buildup currently centred around Latakia," the analysts said.

The Jane's analysts noted "a substantial increase" in the number of Russian combat jets near Latakia, counting four Su-30SM multirole combat aircraft, 12 Su-25 ground attack aircraft and 12 Su-24M attack fighters.

There were also more than 25 fighter and attack aircraft, 15 helicopters, nine tanks, three surface-to-air missile systems and at least 500 personnel on the ground in Syria, according to the report.

Citing two US officials, CNN said Russia also appeared to be conducting surveillance operation as unmanned aircraft were spotted over Syria.

Russia's recent activities amid the volatile Syrian conflict are fuelling fears of a possible miscalculation that could further worsen hostilities in the region.

Rami Abdelrahman, director of the Syrian Observatory of Human Rights, said raids and airstrikes against the ISIS have become more precise with the Russian reinforcements and efficient equipment.

Aljazeera reported that 38 ISIS fighters have died over the last 24 hours as the Assad government launched airstrikes against the group in Palmyra and two other towns in the Homs province,

However, 12 civilians were also killed and ten others injured in Palmyra, said the British-based observatory. Many of the wounded are reportedly dying due to a lack of basic medical supplies in the city.

Pentagon spokesman Peter Cook said the United States is closely monitoring the situation in Syria but admitted that US officials "still do not have an entirely clear picture of exactly what the Russians are hoping to do in Syria.''

He said Pentagon officials believe "there may be an opportunity for the Russians to play a constructive role" in the fight against ISIS.

Retired. Gen. David Petraeus, former commander of US forces in both Iraq and Afghanistan, expressed belief that Moscow's move was "to shore up the al-Assad regime in order to preserve Russian influence in the Middle East."