A Syrian government assault on the rebel bastion of Al-Qusayr raged into a second day on Monday, with at least 28 members of the Lebanese Shiite group Hezbollah reportedly killed as they fought alongside the army.
The battle began on Sunday, when government troops backed by regime ally Hezbollah stormed the western town, a strategic prize in the country's two-year conflict.
The fighting has raised fears of a "massacre" and cast a shadow over US-Russian efforts to organize a peace conference to discuss a political solution to the war.
The Syrian Observatory for Human Rights said the fighting had left at least 56 rebels dead, six of them on Monday, and four civilians, including one woman.
Quoting "reliable sources," it said that "28 members of Hezbollah's elite forces were killed and more than 70 others wounded in clashes in the town of Qusayr yesterday," Sunday.
"The death toll is expected to rise because three of the wounded are in serious condition."
A source close Hezbollah told AFP at least 20 members had been killed in Syria, with around 30 more wounded.
The attack began with an early-morning offensive on Sunday led by warplanes and heavy artillery fire, with ground troops moving in afterwards.
"We struck from several fronts -- south, east and northeast," one soldier told state television from the rebel bastion.
A military source told AFP government forces controlled the center of Al-Qusayr and the Syrian flag was flying over the recaptured town hall, though activists denied troops had advanced that far.
Opposition activist Hadi al-Abdullah said the assault was terrifying.
"Yesterday was the most violent, most difficult day in the whole of the Syrian revolution," he told AFP.
"I've never seen so much shelling... Al-Qusayr was being shelled from all sides."
Al-Qusayr is considered strategically important because it sits between Damascus and the coast and near the Lebanese border.
"If the army manages to take control of Al-Qusayr, the whole province of Homs will fall," said Observatory director Rami Abdel Rahman.
The regime has made recapturing Al-Qusayr and nearby rebel areas of Homs province a key objective, and fighting has raged in the region for months.
The pro-regime daily Al-Watan touted the army's progress on Monday.
"We are just a few hours or days away from the announcement of the restoration of security in the town of Al-Qusayr after the Syrian Arab army took control of most of the key areas of the town," it said.
The assault on Al-Qusayr drew condemnation and concern from opponents of Syria's President Bashar al-Assad and international capitals.
The umbrella opposition National Coalition warned "there are clear indications that a civilian massacre will soon take place."
"The Syrian Coalition calls on the Arab League and its secretary general to hold an emergency meeting of Arab foreign ministers to take the necessary precautions to protect Al-Qusayr," it said in a statement.
"The Syrian Coalition also asks the international community to take responsibility for protecting the lives of the 40,000 civilians in Al-Qusayr," it added, calling for UN condemnation of Hezbollah's role in the fighting.
Earlier, the Syrian National Council, a Coalition member, warned the assault endangered efforts to organize a peace conference.
"We say to the countries that are working for a political solution in Syria that allowing this invasion to go ahead in silence... will render any conference and any peace effort meaningless."
In the UAE, Foreign Minister Sheikh Abdullah bin Zayed al-Nahayan called for "the repressive machine in Damascus" to be stopped.
And France's foreign ministry called for "all the players in a position to avoid a new massacre of the Syrian civilian population to mobilize without delay."
The United States, which backs the uprising and Russia, a staunch regime ally, are working to organize a peace conference next month despite their opposing loyalties.
But the prospects for success seem dim, with President Assad telling Argentine media over the weekend that he would not step down -- a key opposition demand.
At least 164 people were killed throughout the country on Sunday, the Observatory said. The group says that more than 94,000 people have been killed since the uprising began in March 2011.