Kerry tells Lavrov any involvement could escalate conflict during phone call to discuss reports of military build-up.
US President Barack Obama has warned that Russia’s decision to send military staff and equipment to Syria reflected a strategy that was “doomed to fail”.
“The strategy that they are pursuing right now, doubling down on (Bashar al) Assad, I think is a big mistake,” he said on Friday, warning Moscow was “going to have to start getting a little smarter”.
Earlier in the day, Russian Foreign Minister Sergei Lavrov said that the Kremlin would continue to supply weapons to the Syrian government, following warnings from US and NATO over Moscow’s increasing involvement in the Syrian conflict.
Lavrov told a news conference that Russia was conducting military exercises in the Mediterranean Sea, that it had been for some time, and that the exercises were in line with international law.
The minister also called on other world powers to help arm the Syrian military, which he described as the most efficient force against the Islamic State of Iraq and Levant (ISIL) group.
The statement came a day after Lavrov confirmed that the country’s “humanitarian” flights to Syria carried military equipment as well as humanitarian aid.
“Russian planes are sending to Syria both military equipment in accordance with current contracts and humanitarian aid,” Lavrov told reporters on Thursday.
Russia’s Kommersant daily newspaper said earlier on Thursday that Moscow’s advanced BTR-82A armoured personnel carriers were among arms supplied to Damascus.
Moscow has previously insisted in public that its flights to Syria were only for humanitarian purposes.
Al Jazeera’s Peter Sharp, reporting from Moscow, said that “nothing much has really changed” as the Russians had been supplying the Syrian government with arms, advisers and other military equipment for about 60 years.
Russian military support
“Between 2009 and 2011 Russia was supplying 71 percent of Syria’s military needs – everything from jets to military equipment to air defence systems.
“The Russian foreign minister says this continues to take place but he did make a distinction. There has been additional air traffic coming into Latakia’s airbase and he says military equipment and humanitarian aid are being delivered,” Sharp said.
“As far as boosting boots on the ground, he said Russian military specialists are working on training Syrians on using Russian weapons and no additional steps have been taken.”
The Kremlin declined to comment on Thursday on whether Russian troops were fighting in Syria, after sources in Lebanon told the Reuters news agency that Russian forces had begun participating in military operations there.