Updated

Reports of Russian anti-terror troops on the ground in Syria is raising new concerns about whether Russia's policies are indirectly, or even directly, enabling the brutal crackdown on Syrian protesters.

Russia's Defense Ministry acknowledged Monday that the navy's Iman oil tanker arrived at the Syrian port of Tartus 10 days ago on a mission to assist Russian navy ships on anti-piracy patrols in the Gulf of Aden and “for demonstrating the Russian presence in the turbulent region and possible evacuation of Russian citizens," the Black Sea Fleet told Interfax news agency.

A ministry spokesman would not say how many troops are on board, but Russian news reports suggest a more active military presence in Syria.

Russia is a strong ally to Syrian President Bashar Assad and has angered fellow members of the United Nations Security Council by blocking repeated attempts to put an end to violence in Syria.

A Security Council source told ABC News that the arrival of members of Russia’s military in Syria was a “bomb” of a development, sure to have serious repercussions.

Interfax reported the tanker arrived in Tartus on the Mediterranean Sea with an anti-terror squad from the Russian Marines.

ABC News reported that RIA Novosti, a news outlet tied to the Kremlin, announced the arrival only on its Arabic-language website.

Russian embassy officials have declined to comment, but Russian Foreign Minister Sergei Lavrov last week told a meeting of the Russian State Duma that there were no plans for sending combat troops to Syria, according to RIA Novosti.

“As for the question whether I consider it necessary to confront the United States in Syria ... to take part in military actions, no. I believe this would be against Russia’s national interests,” Lavrov said.

Valentina Matviyenko, speaker of the Russian parliament’s upper house, said last week that a government delegation would visit Syria this week for discussions with representatives from Assad’s cabinet and opposition groups, according to RIA Novosti.

Russian Defense Minister Anatoly Serdyukov denied reports that special forces were inside Syria, although he said there are military and technical advisers in the Syria.

The port of Tartus is now the only naval base Russia has outside the former Soviet Union. A Russian navy squadron made a call there in January in what was seen by many as a show of Moscow's support for Assad.

The Associated Press contributed to this report.