By Alexei Anishchuk and Steve Gutterman
MOSCOW (Reuters) - Russia said the chances of Syrian President Bashar al-Assad staying in power were growing "smaller and smaller", as fighting on Sunday in southwestern Damascus shut a main highway from the capital.
Assad has long counted Moscow as an ally and Prime Minister Dmitry Medvedev's remarks were the most vocal Russian statement yet that his days may now be numbered, although they come after predictions from France, an avowed enemy, and from neighboring Jordan that the Syrian president's downfall is not imminent.
"I think that with every day, every week and every month, the chances of his preservation are getting smaller and smaller," Medvedev said, according to the transcript of an interview in Russian with CNN that was released by his office.
"But I repeat again, this must be decided by the Syrian people. Not Russia, not the United States, nor any other country," said Medvedev, whose administration has criticized Western, Turkish and Gulf Arab support for Syria's rebels.
"The task for the United States, the Europeans and regional powers ... is to sit the parties down for negotiations, and not just demand that Assad go and then be executed like Gaddafi or be carried to court sessions on a stretcher like Hosni Mubarak."
After Egypt's veteran president Hosni Mubarak was toppled, Russia withheld its veto on a U.N. Security Council resolution authorizing Western and Arab powers to provide military help to the rebels who overthrew Muammar Gaddafi in neighboring Libya.
Moscow has since accused the West of breaching sovereign rights and has vetoed U.N. action against Assad. Medvedev warned that removing Assad by force would mean "decades" of civil war.
Russia has been Assad's most important ally throughout the 22-month-old Syrian conflict, which began with peaceful street protests and evolved into an armed uprising against his rule.
Moscow has blocked three Security Council resolutions aimed at pushing him out or pressuring him to end the bloodshed which has killed more than 60,000 people. But Russia has also distanced itself from Assad by saying it is not trying to prop him up and will not offer him asylum.
The mainly Sunni Muslim rebels have seized territory in the north of the country, including several border crossings, and have challenged Assad's control over Syria's main cities.
But Assad's air power and army, whose senior ranks are dominated by his Alawite minority, have stemmed rebel advances.
France said on Thursday there was no sign Assad was about to be overthrown, reversing previous statements that he could not hold out long, and Jordan's King Abdullah said Assad would consolidate his grip for now.
"Anybody who is saying the regime of Bashar has got weeks to live really doesn't know the reality on the ground," Abdullah said in Davos on Friday. "They still have capability, so I give them a strong shot at least for the first half of 2013."
Activists said rebels clashed with forces loyal to Assad in southwestern Damascus on Sunday, seizing a railway station and forcing the closure of the main highway to Deraa in the south.
Footage posted on the Internet showed what activists said was a rebel attack on the station in Qadam district. One clip showed gunmen taking cover as gunfire could be heard. Another showed gunmen inspecting buildings by the track after what the narrator describes as the "liberation" of the station.
Another video showed black smoke billowing above concrete buildings, the result of what activists said was an air strike by Assad's air force near the railway terminal.
Syrian media did not comment on the fighting around Qadam and restrictions on independent media make it difficult to verify reports from activists.
The Syrian Observatory for Human Rights, a British-based opposition group which monitors the violence in Syria, said jets and artillery also struck targets in rebel strongholds to the east and south of the capital after fierce clashes there.
The fighting came as United Nations humanitarian chief Valerie Amos visited Syria ahead of a U.N. aid conference in Kuwait which aims to raise $1.5 billion for millions of people made homeless, hungry and vulnerable by the conflict.
On Wednesday, Amos said Syrians were "paying a terrible price" for the failure of world powers to resolve the conflict, pointing to 650,000 refugees who have fled the country and the millions affected inside Syria.
"Four million people need help, two million are internally displaced and 400,000 out of 500,000 Palestinian refugees have been affected," she told an economic forum in Switzerland.
The United Nations and aid groups inside Syria, including the Syrian Arab Red Crescent, could not keep pace with the rising number of people in need, she said.
"We must find ways to reach more people, especially in the areas we are still unable to get to, and where there is ongoing fighting," she said.
Last month, the United Nations withdrew 25 of its 100 foreign aid workers from Syria as fighting intensified around Damascus, but Amos said it remained committed to maintaining aid work.
Most of the money from the Kuwait conference will go to support neighboring countries hosting hundreds of thousands of refugees, while $519 million is earmarked for aid inside Syria.
The fighting has alarmed neighboring Israel, where Vice Prime Minister Silvan Shalom said that any sign that Syria's grip on its chemical weapons was slipping could trigger Israeli military strikes.
Should Lebanon's Hezbollah guerrillas or Syrian rebels obtain Syria's chemical weapons, "it would dramatically change the capabilities of those organizations," Shalom said.
Such a development would be "a crossing of all red lines that would require a different approach, including even preventive operations," he told Israel's Army Radio.
Assad has vowed to defeat rebels he describes as terrorists. In a speech three weeks ago he repeated his readiness for a national dialogue, but ruled out talking to "extremists who don't believe in any language but killing and terrorism".
State television said on Sunday that Syria's highest judicial council had suspended legal cases against Syrian opposition members so they can take part in talks - a proposal roundly rejected by most of Assad's opponents.
Medvedev said Assad did not appear to be ready for a negotiated solution to the crisis.
"He should have done everything much faster, attracting part of the moderate opposition, which was ready to sit at the table with him, to his side," the Russian premier said. "This was his significant mistake, and possibly a fatal one."
But he also warned of consequences if Assad is thrown out by force. He said: "Then the civil war will last for decades."
(Additional reporting by Dominic Evans in Beirut, Alistair Lyon in Amman, Dan Williams in Jerusalem; Writing by Dominic Evans; Editing by Alastair Macdonald)