Russia tells U.S.: Syria activity 'defensive in nature'

"He said that the Russian activities were defensive in nature and that they were designed to honor commitments made to the Syrian government," the official said, speaking to reporters on condition of anonymity, without elaborating.

Washington has voiced concern about Russia's military buildup in Syria, which the Pentagon has said appears to be designed at establishing an air operations hub in the country.

(Reporting by Phil Stewart; Editing by Eric Walsh)