MOSCOW (AFP) - Russian's military on Thursday blasted targets across Syria with long-range strategic bombers for a third day, the defence ministry said, as Moscow pressed on with its intensified air campaign in the country.

Strategic bombers flying over Russian territory unleashed 12 cruise missiles at Islamic State in Iraq and Syria (ISIS) group targets including warehouses and command posts in the Idlib and Aleppo provinces as they launched their "third massive air strike", the defence ministry said in a statement.

Powerful long-distance Tu-22 bombers also struck six targets including three "major plants" for refining oil in ISIS strongholds in the Raqa and Deir Ezzor provinces, Moscow said.

Meanwhile, jets stationed at Russia's base in government-held territory in Syria hit 138 targets around the country on Thursday, the statement said.

Moscow ratcheted up its bombing campaign in Syria on Tuesday after confirming for the first time that a Russian passenger plane that crashed in Egypt last month was brought down by a bomb.

Russia first launched air strikes on Syria in September at the request of its long-standing ally President Bashar al-Assad, while a US-led coalition of countries opposed to the Syrian strongman is conducting a separate air campaign against ISIS.