World Bulletin / News Desk
In a written statement, the ministry said reports of seven fighter jets being destroyed were "fake" news.
Russian Kommersant newspaper reported earlier that seven Russian military planes had been destroyed and more than 10 military personnel killed in the mortar attack.
On Wednesday, the ministry said two pilots died when a Russian Mi-24 helicopter crashed due to a technical fault 15 kilometers (9.3 miles) off the Khmeimim Air Base.
The ministry had denied the helicopter crashed following an attack. A Syrian local source said the crash took place on Dec. 31, 2017.
Last month, Russia announced it was withdrawing the bulk of its forces from Syria after it had been fully liberated of Daesh elements.
In October 2017, the crew of a Russian Su-24 warplane were killed when the jet crashed upon takeoff from Khmeimim.