Russian experts are in Syria to oversee arms deliveries from Moscow, says Foreign Ministry spokesperson Maria Zakharova. The remarks are the the first official confirmation of the Russian presence, Reuters reports.

The revelation came a day after the United States asked Bulgaria and Greece to close their airspaces to two Russian transport planes that were bound for Syria, according to the New York Times.

Bulgaria agreed with Washington and denied air-access to the planes, citing fears that Russia was not transporting humanitarian aid as Moscow has claimed. Greece has not yet responded publicly.

Russia and the United States have not been able to agree on a solution to the conflict in Syria. Both see ISIS as a threat. But the two nations disagree on how to confront the terrorist group and the future of Syrian president Bashar al-Assad’s regime.

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Write to Mark Rivett-Carnac at mark.rivett-carnac@timeasia.com.