The Syrian regime continued its deadly assault on its own citizens Saturday, killing dozens of people a day before a constitutional referendum on a measure the president says will open up his country's political system.

At least 89 people were killed across the country Saturday, as Syrian regime rockets bombarded the opposition stronghold of Homs for a fourth week in a row as human rights leaders begged for help from inside the besieged city.

The violence occurred a day before Syrians are to vote on a revised charter put forward by President Bashar Assad, changes that would create a multi-party system. Syria has been ruled by the same family since 1963, when the president's father, Hafez, took power in a coup.

Opposition and rebel leaders have denounced the measure as a ploy and have called for a boycott of the vote.

"How can they ask us to talk about a new constitution when they are shelling our neighbourhood?" said Abu Mohammed Ibrahim from the embattled Homs neighbourhood of Baba Amr.

"They are hitting us with all types of weapons. What constitution? What referendum?"

Posters around the capital of Damascus, where Assad has some degree of support among businesspeople and minority religious groups, urged citizens to cast their ballots.

Syrian Interior Minister Lt. Gen. Mohammed al-Shaar said more than 14,000 voting centres have been set up, and more than 14 million Syrians are eligible to cast ballots.

Despite the pending vote, Syrian forces continued to hammer Homs, where 19 people are believed to have died Saturday.

Earlier in the day, human rights worker Sami Ibrahim told CTV News Channel that people are trapped in their homes and thousands need immediate humanitarian assistance.

"They are staying inside their houses," he said in a telephone interview from Syria. "They are afraid to go outside. If you want to walk to your car or something like that, the rockets will shoot you . ... If you want to help your neighbour you will be unable."

The International Committee of the Red Cross said Saturday it was unable to gain access to the besieged Homs neighbourhood of Baba Amr to evacuate wounded civilians, including two journalists who were injured in heavy shelling earlier this week.

The organization managed to help 27 people flee Homs on Friday, and had evacuated others from various parts of the country. But ICRC spokesperson Hicham Hassan said negotiations to allow the agency into Baba Amr had "yielded no concrete results."

The agency was still working to remove the bodies of American journalist Marie Colvin and French photojournalist Remi Ochlik, who were killed in Homs on Wednesday.

The British-based Syrian Observatory for Human Rights said the death toll was at least 89, including well-known citizen journalist Anas al-Tarshi, who filmed attacks in Homs and posted them to activists' websites. The agency said al-Tarshi was helping transport the injured to a field hospital when a shell struck his car.

The bombardment came just one day after an ambitious 60-nation conference met in Tunis to find solutions to end the year-long violence, which has killed more than 5,400.

But opposition activists inside Syria say the situation is deteriorating daily. They accused the outside world of abandoning them to forces loyal to Assad.

"They (foreign leaders) are still giving opportunities to this man who is killing us and has already killed thousands of people," said activist Nadir Husseini.

The Tunis conference – attended by U.S. Secretary of State Hillary Clinton and Canadian Foreign Minister John Baird – concluded with no action plan, although there were suggestions to smuggle arms to Syrian rebels and send humanitarian aid.

Several nations called for a civilian United Nations peacekeeping mission to deploy once the violence ends.

Saudi Arabia has been a vocal critic of the Assad regime, and Foreign Minister Saud al-Faisal told the conference that he supported arming opposition groups in the country.

"I think it's an excellent idea," he told reporters. When asked why, he replied: "Because they have to defend themselves."

The comments earned a stern rebuke from the Syrian regime, with state-run newspaper Al Thawra accusing the Saudi prince of being a "direct partner in shedding more Syrian blood."

"It's shameful for the vocabulary of the Saudi speech to reach this level ... and to announce so rudely support for terrorists," a Saturday commentary in Al Thawra said. The paper is a mouthpiece for the Syrian government.

Neither China nor Russia participated in the Tunis summit and Clinton denounced both countries for previously blocking the United Nations Security Council from taking action to stop the massacres in Syria.

"They are clearly not on the side of the Syrian people," Clinton said.

China responded with strong language of its own, saying the U.S. and Europe have their own agenda in Syria, saying the two countries "harbour hegemonistic ambitions."

China's state news agency said its position on Syria was balanced and that "most of the Arab countries have begun to realize that the United States and Europe are hiding a dagger behind a smile.

"In other words, while they appear to be acting out of humanitarian concern, they are actually harbouring hegemonistic ambitions," it said.

U.S. President Barack Obama, meanwhile, vowed the U.S will keep up pressure on Syria's leader to stop the "slaughter" of civilians.

Obama said Saturday it is "imperative" the world unite in condemning the Syrian military onslaught on civilians.

"It time to stop the killing of Syrian citizens by their own government," he said. But he didn't give specifics about what the U.S. or other countries could really do to help.

In Tunis, Canadian Foreign Affairs Minister John Baird joined in pressing the Assad regime to open the country to international assistance and pledged $1.5-million in Canadian aid.