The senior executive, who requested anonymity, said the United States has passed through Russia "regret" for the "unintended loss of life" in the forces of the Syrian Army fighting against the Islamic State (EI).
The official gave no number of dead and wounded in the attack, although the Russian Defense Ministry said 62 Syrian soldiers were killed by the bombing of the international coalition, produced about 17.00 Moscow time (14.00 GMT) near the airport Deir ez-Zor in eastern Syria.