Since admitting that it was indeed assisting the Syrian regime under President Bashar Assad with military support, Russia has phenomenally expanded its air base in Syria, where it has sneaked in at least 48 military aircraft and attack helicopters.

Kremlin that has for long remained a  strong ally of the Assad regime, took many by surprise as it ramped up its air defence capabilities in Syria over the weekend. Reports indicate Russia now will be able cover more grounds in its fight alongside the Assad regime to eradicate the Islamist rebels, including the Islamic State (Isis) militants.

According to Jerusalem-based military intelligence website DEBKAfile, Russia has sneaked in 28 combat aircraft and 16 helicopters at its air base located near Latakia. Citing unnamed US national security sources, the website noted that to avoid detection, Russian military aircrafts were made to fly behind the giant Antonov-124 transport aircraft.

The speed at which Russia has strengthened its air defence inside Syria has taken US by surprise, the report noted.

The New York Times noted that the "sharp" increase in the number of combat aircrafts will give Russia "new ability" to strike targets on ground in the war-ravaged country.

Till last week, Russia only had four Russian Su-30SM air-to-air fighters in Syria, however, now 28 Sukhois are stationed at Latakia Russian air base along with 16 attack helicopters.

A dozen Sukhoi Su-24 -- a powerful long-range, low-level strike attack aircraft with real all-weather precision attack -- and Sukhoi Su-25 Frogfoot, which is the mainstay of Russian ground-attack regiments, are part of the Russian fleet in Syria.

Russia, which is planning to deploy combatant units from Russian Marine Brigades 810 and 336, also is building a ground base in Jablah, where it will deploy advanced S-300 air defence missile systems.

A Russian MiG-31 interceptor has also been put on standby at the Mezza airbase in Damascus.