A small contingent of combat forces was aboard the vessel headed for Tartus, which hosts a Cold War-era naval supply and maintenance base staffed by Russians under a 1971 agreement with Syria, NBC News quoted U.S. officials as saying.
U.S. officials also backpedaled on charges Russia was sending attack helicopters to Syria to help prop up the regime of Bashar Assad. Rather, the officials said, Russia had shipped replacement parts for choppers already in use by Damascus.
The head of the United Nations monitoring mission in Syria Friday accused both the government and rebels of escalating violence in the country in recent days.
Norway Maj. Gen. Robert Mood's assessment came six weeks after U.N. monitors began deploying to Syria under a peace plan proffered by U.N.-Arab League envoy Kofi Annan, The New York Times reported.
"Violence over the past 10 days has been intensifying willingly by both parties, with losses on both sides and significant risks to our observers," Mood said. "There seems to be a lack of willingness to see a peaceful way forward. Instead, there is a push toward advancing military positions."
U.N. observers said the Syrian town of Haffeh appeared deserted, with many buildings torched and the "strong stench of dead bodies" hanging in the air.
The observers, part of the mission to monitor an all-but-ignored U.N.-Arab League-backed cease-fire, finally entered the town after being impeded by violence in the area, the United Nations said.
When they reached the site, the observers said, most government institutions were set on fire, stores were looted and burned and residential homes appeared burglarized.
"A strong stench of dead bodies was in the air and there appeared to be pockets in the town where fighting is still ongoing," U.N. Supervision Mission in Syria spokeswoman Sausan Ghosheh, said. "The number of casualties is still unclear."
The observers also reported Baath Party headquarters was shelled and appeared to be the scene of heavy fighting, saying remnants of heavy weapons and other weaponry were found in the town.
"UNSMIS is deeply concerned about the escalating level of violence in Syria and calls on all parties to put down their weapons and choose the path of non-violence for the welfare of the Syrian people who have suffered enough," Ghosheh said.
The U.N. observers are tasked with monitoring the cessation of violence in Syria, as well as monitoring and supporting the implementation of the six-point peace plan proffered by Annan. Among other things, the peace plan calls for an end to violence, access for humanitarian agencies to provide relief to those in need, the release of detainees, the start of inclusive political dialogue that takes into account the aspirations of the Syrian people and unrestricted access to the country for the international media.
The United Nations estimates that more than 10,000 people, mostly civilians, have been killed and tens of thousands displaced in Syria since the uprising against President Bashar Assad began in March 2011.
The Syrian Network for Human Rights and the Damascus Center for Human Rights Studies reported Friday they documented five casualties in different Syrian cities.
The organizations said government forces killed two people in Deir Ezzor, one in Idleb and two in and around Damascus.
Syrian authorities said they arrested an al-Qaida terrorist who planned to blow himself up in a Damascus mosque when it was most crowded Friday.
The man, identified by the state-run Syrian Arab News Agency as Mohammad Houssam al-Sadaki, "confessed that there are other persons supposed to explode themselves in a number of Damascus mosques today during Friday prayers," the news agency said.
SANA reported al-Sadaki said he "was given an explosive vest as to explode himself inside al-Rifae Mosque during ... Friday noon prayers when the mosques are usually very crowded."
Syria blames the country's violence on "armed terrorist groups."