A United Nations Security Council source told ABC News the development was 'a bomb' certain to have serious repercussions.
Russia is one of President Bashar al-Assad's strongest allies despite international condemnation of the government's violent crackdown on the country's uprising.
Attempts by the United Nations Security Council to halt the violence have been repeatedly blocked by Russia which has accused the U.S. and its allies of trying to start another war.
Now the Russian Black Sea fleet's Iman tanker has arrived in the Syrian port of Tartus on the Mediterranean Sea.
An anti-terror squad from the Russian Marines is aboard, according to the Interfax news agency. Read More