REUTERS

The officials said that Russia had deployed four additional attack aircraft to its coastal airbase in Syria earlier this week. One official said the jets had stopped in Iran to refuel before continuing on to Syria, Fox News reported.

"[The Russians] say they are pulling out, but we have seen no evidence to support that. On the contrary, we have seen new things coming in," said one official.

Read alsoIsraeli satellite spots Russian Iskander missiles - mediaThe four Russian Su-25 jets, known as Frogfoots by NATO – arrived Monday, according to one official. The Su-25, similar to the U.S. Air Force's A-10, is used for close air support. The Russian jet has reinforced armor siding to protect the pilots from ground fire.

One official also said the Russians have deployed additional Russian civilian contractors, as well as fighters from Chechnya, but would not provide any specific numbers.

The Russian military maintains roughly 36 fighter jets and helicopter gunships in Syria, a number unchanged in the last month, according to officials.

Putin ordered the military reduction in Syria in late December following the announcement of a new cease-fire agreement with Iran and Turkey.