The Syrian government is holding a referendum on a new constitution as violence continues around the country, killing at least 20 people.The new constitution calls for a multi-party parliamentary election within three months.The opposition has boycotted the vote, calling it a farce and demanding President Bashar al-Assad stand down.US Secretary of State Hillary Clinton has said "there’s every possibility” Syria could descend into civil war.But she warned "outside intervention” could exacerbate the situation. "I think that as you try to play out every possible scenario, there are a lot of bad ones that we are trying to assess,” she told the BBC.Activists say more than 89 people died across Syria on Saturday.‘Laughable’The Syrian government has pressed ahead with organising the referendum despite the unrest, setting up more than 13,000 polling stations for 14.6m voters.Voting began at 07:00 (05:00 GMT) and polling stations are due to stay open for 12 hours.State television showed people voting in Damascus and various other places, and it all looked fairly normal, the BBC’s Jim Muir reports from neighbouring Lebanon.But, he added, in many other parts of the country, it is far from normal, with explosions and shooting reported from the east, west, north and south - in areas where violence has been going on for months.At least nine civilians and four soldiers were killed in the embattled city of Homs, the UK-based activist group, Syrian Observatory for Human Rights, said.Violent clashes were reported in the central city of Hama, the north-western province of Idlib and in Daraa province, south of Damascus.