(Reuters) - At least 59 Syrian civilians and soldiers were killed Sunday in bloodshed that coincided with a vote on a new constitution that could keep President Bashar al-Assad in power until 2028.

Assad says the referendum shows his commitment to democratic reform while Western powers and Syrians involved in an 11-month-old revolt against his rule have described it as a farce.

The Syrian Observatory for Human Rights said a military bombardment of opposition districts in the city of Homs had killed 12 civilians while security forces killed three people when they opened fire on a demonstration in Damascus.

The British-based Observatory said 21 other civilians died and rebels killed 23 members of the security forces across Syria, scene of what has become an increasingly militarized revolt against four decades of Assad family rule.

Voting took place in the referendum on a new constitution, which Assad says will lead to a multi-party parliamentary election in three months. The result is expected to be announced on Monday.

What should we be voting for, whether to die by bombardment or by bullets? This is the only choice we have, said Waleed Fares, an activist in the Khalidiyah district of Homs, where bombardment is now in its fourth week.

We have been trapped in our houses for 23 days. We cannot go out, except into some alleys. Markets, schools and government buildings are closed, and there is very little movement on the streets because of snipers, he said.

He said another besieged and battered district, Baba Amro, had had no food or water for three days. Homs in general has no electricity for 18 hours a day. Tight curbs on independent reporting in Syria make witness reports hard to verify.

Elsewhere in Homs, rebel fighters burned a building of Assad's ruling Baath Party in the Hamidiyeh district of the old city and attacked an armored vehicle, the Observatory said.

The Interior Ministry acknowledged obliquely that security conditions had disrupted voting, saying: The referendum on a new constitution is taking place in a normal way in most provinces so far, with a large turnout, except in some areas.

The Syrian government, backed by Russia, China and Iran, and undeterred by Western and Arab pressure to halt its assaults, says it is fighting foreign-backed armed terrorist groups.

NO DESIRE FOR REFORM

Syria's Prime Minister Adel Safar, asked about opposition calls for a boycott, said this showed a lack of interest in dialogue. There are some groups that have a Western and foreign agenda and do not want reforms in Syria and want to divert Syria's steadfastness, he told reporters in Damascus.

We are not concerned with this. We care about ... spreading democracy and freedom in the country, Safar said.

If there was a genuine desire for reform, there would have been movement from all groups, especially the opposition, to start dialogue immediately with the government to achieve the reforms and implement them on the ground.

The outside world has been powerless to restrain Assad's drive to crush the revolt, which has the potential to slide into a sectarian conflict between Syria's Sunni Muslim majority and the president's minority Alawite sect.

Unwilling to intervene militarily and unable to get the U.N. Security Council to act in the teeth of Russian and Chinese opposition, Western powers have imposed their own sanctions on Syria and backed an Arab League call for Assad to step down.

While the West dismisses talk of a Libya-style NATO role to support Assad's opponents, Gulf Arab states have pushed for a more forceful stance. Saudi Arabia said on Friday it would back the idea of arming rebels - a proposal likely to alarm Moscow.

I very much hope the United States and other countries ... do not try to set a military scenario in motion in Syria without sanction from the U.N. Security Council, Russian Prime Minister Vladimir Putin said.

U.S. Secretary of State Hillary Clinton said that any foreign intervention could just fuel further violence.

I think there is every possibility of a civil war. Outside intervention would not prevent that, it would probably expedite it, she told BBC television in an interview.

We have a very dangerous set of actors in the region: al Qaeda, Hamas and those who are on our terrorist list claiming to support the opposition. You have many Syrians more worried about what could come next ...

If you bring in automatic weapons, which you can maybe smuggle across the border, what do they do against tanks and heavy artillery? There is such a much more complex set of factors.

German Foreign Minister Guido Westerwelle said Sunday's referendum was nothing but a farce.

Sham votes cannot contribute to a solution of the crisis. Assad needs to put an end to the violence and clear the way for a political transition, he said in a statement.

HARROWING CONDITIONS

The military onslaught on parts of Homs has created harrowing conditions for civilians, rebels and journalists.

A video posted by activists on YouTube showed Mohammad al-Mohammad, a doctor at a makeshift clinic in Baba Amro, holding a 15-year-old boy hit in the neck by shrapnel and spitting blood.

It is late at night and Baba Amro is still being bombarded. We can do nothing for this boy, said the doctor, who has also been treating Western journalists wounded in the city.

American correspondent Marie Colvin and French photographer Remi Ochlik were killed in the bombardment of Homs last week and two other Western journalists were wounded. The group is still trapped there despite Red Cross efforts to extricate them.

The International Red Cross and Syrian Arab Red Crescent could not get into Baba Amro on Sunday and were still negotiating with authorities and opposition, the ICRC said.

Syrian authorities had not responded to a request for a ceasefire to allow the wounded to be evacuated, it added, and conditions were worsening by the hour.

Whether they are women, children, men, Syrian journalists, or foreign journalists, all have the same status. They need to reach medical facilities regardless of their status without any distinction, ICRC chief spokeswoman Carla Haddad said.

In Hama, another city with a bloody record of resistance to Baathist rule, one activist said nobody was taking part in the referendum. We will not vote on a constitution drafted by our killer, he said by satellite telephone, asking not to be named.

If the constitution is approved in the vote, a foregone conclusion, it would drop an article making Assad's Baath party the leader of state and society, allow political pluralism and enact a presidential limit of two seven-year terms.

But the limit will not be enforced retrospectively, meaning that Assad, already in power for 11 years, could serve another two terms after his current one expires in 2014.

Dozens of people lined up to vote in two polling stations visited by a Reuters journalist in Damascus. I've come to vote for President Bashar, God protect him and give him victory over his enemies, said Samah Turkmani, in his 50s.

Another voter, Majed Elias, said: This is a national duty, whether I agree or not, I have to come and vote.

This is Syria's third referendum since Assad inherited power from his late father. The first installed him as president in 2000 with an official 97.29 percent 'Yes' vote. The second renewed his term seven years later with 97.62 percent in favor.

(Additional reporting by Khaled Yacoub Oweis in Amman, Mariam Karouny, Erika Solomon and Dominic Evans in Beirut, Christian Ruettger in Berlin and Arshad Mohammed in Rabat and Stephanie Nebehay in Geneva; editing by Andrew Roche)