The United Nations General Assembly is becoming the focus of attempts to apply pressure on the Syrian government over its continued crackdown on dissent.
Saudi Arabia is circulating a draft resolution calling for an end to violence by all sides and for President Bashar al-Assad to step aside.
It is similar to one which Russia and China vetoed in the Security Council.
The diplomatic move came as Syrian tanks and artillery continued to bombard parts of the city of Homs.
Opposition activists said the Baba Amr district - a centre of anti-government protests - had been hit by mortars on Saturday, killing at least 15 people, and that army snipers had been deployed on rooftops.
After a week under shellfire and virtual siege, conditions in Homs are reported to be getting desperate, with basic supplies running low.
Meanwhile, Syria's state news agency reported that the director of the Hamish military hospital in Damascus, Brigadier Dr Isa al-Kholi, had been shot dead on Saturday by an "armed terrorist group" outside his home in the capital's northern Rukn al-Din district.
The BBC's Jim Muir, in neighbouring Lebanon, says that although several officers of similar rank have been killed in combat in recent weeks, this is believed to be the first assassination of such a senior military figure in Damascus since the uprising against President Assad began in March.
On Friday, activists said at least 52 people were killed across the country by security forces, including 16 in Homs and 15 in suburbs of Damascus.
Human rights groups say more than 7,000 have died since March. The government says at least 2,000 members of the security forces have been killed combating "armed gangs and terrorists".
The UN General Assembly is scheduled to discuss Syria on Monday, when it will be addressed by the UN's High Commissioner for Human Rights, Navi Pillay, but no vote on the resolution is expected by then.
There is no power of veto at the General Assembly but its resolutions have no legal force, unlike those of the Security Council.
The draft resolution circulated by Saudi Arabia "fully supports" the Arab League peace plan published last month, which called on Mr Assad to hand over power to his vice-president, and make way for the rapid formation of a national unity government including the opposition.
While calling for an end to the violence by all sides, it lays blame primarily on the Syrian authorities, which are strongly condemned for "continued widespread and systematic violations of human rights and fundamental freedoms".
The draft urges accountability for those guilty of human rights violations, but does not specifically mention the International Criminal Court.
There is also a request for Secretary General Ban Ki-moon to appoint a special envoy to promote a peaceful solution to the crisis - a proposal that Arab League Secretary General Nabil al-Arabi made this week.
The US ambassador to Syria, Robert Ford, on Friday posted satellite imagery on Facebook which he said showed heavy weaponry deployed outside urban areas, including Homs, Zabadani, Rankun and Halban.
"When we see disturbing photos offering proof that the regime is using mortars and artillery against residential neighbourhoods, all of us become even more concerned about the tragic outcome for Syrian civilians," he wrote.
"It is odd to me that anyone would try to equate the actions of the Syrian army and armed opposition groups since the Syrian government consistently initiates the attacks on civilian areas, and it is using its heaviest weapons," he added, referring to Russia's belief that the rebels are equally culpable.
The satellite images are dated 6 February - the day the US closed its embassy in Damascus and Mr Ford left Syria, citing security concerns.
Accusations over Aleppo bombing
Meanwhile, the government and rebel Free Syrian Army (FSA), a group of army defectors, blamed each other for two bomb blasts in the city of Aleppo that killed 28 people and wounded more than 200 others.
State television blamed the bombings on what it described as "armed terrorist gangs", which it said had targeted a Military Intelligence complex and a riot police base but killed civilian bystanders, including children.
It broadcast gruesome pictures of the aftermath of the two attacks, with large craters and scattered body parts.
The FSA's deputy leader told the BBC its fighters had been attacking the bases at the time, but were not responsible for the blasts.
Opposition activists in Aleppo also blamed the government, saying it was trying to discredit the uprising. They said there had been suspicious activity by security forces around the two bases before the explosions, and noted that state TV cameras had reached the sites within minutes.
US officials are reported to believe that two recent bombings in Damascus were carried out by militants from al-Qaeda in Iraq, and that the Sunni extremist group was also likely behind the attacks in Aleppo.
The officials cited US intelligence reports, which appeared to support President Assad's accusation that al-Qaeda was involved in attacks on Syrian government forces, according to the McClatchy Newspapers.
The overall leader of al-Qaeda, Ayman Zawahiri, was believed to have authorised al-Qaeda in Iraq's operations in Syria, the officials said.
"This was Zawahiri basically taking the shackles off," one added.
Our correspondent says that such a development would not likely be welcomed by the bulk of the opposition movement, which has struggled for months to keep the uprising confined to peaceful massed protests.