"The Russian support of the Syrian army has tipped the scales against the terrorists," Assad told NBC News.
"At the same time, Turkey and Saudi Arabia have sent more troops since that Russian legal intervention started. But in spite of that, it was the crucial factor," he added.
Bashar Assad said his relationship with Russian President Vladimir Putin is very frank, honest and based on mutual respect.
"Very frank, very honest, mutual respect," Assad told NBC News, answering a question on how he would describe his relationship with the Russian president.
The Syrian leader said he was not worried about Putin's upcoming meeting with US Secretary of State John Kerry and the possibility of Moscow and Washington agreeing on the need for him to resign.
"No, for one reason. Their politics, the Russian politics, [are] not based on making deals, it's based on values," he said.