Fierce fighting has been reported in the strategic Syrian town of Qusair, as rebels and government forces backed by Hezbollah militants fight for control.
The state news agency reported that the army had taken control of most of the town on Monday, and killed more than 100 of what it called "terrorists".
Activists denied that Qusair had been captured, but said some 50 people had died in heavy shelling since Sunday.
They also said at least 23 Hezbollah fighters from Lebanon had been killed.
Qusair, a small town about 30km (18 miles) south-west of the city of Homs, is seen as important to both sides.
It helps link Damascus with government strongholds on the Mediterranean coast, and is a conduit for rebel supplies and fighters from Lebanon, whose border is 10km (6 miles) away.
Fighting has raged for weeks around Qusair, which has been controlled by the opposition to President Bashar al-Assad for several months.
Following a day of heavy bombardment by aircraft and artillery, the army launched an offensive to recapture the town on Sunday. By the evening, they had taken the municipality building in the town centre and were advancing, according to state media.
The claim was denied by opposition activists, although they admitted the rebels had suffered very heavy casualties. They posted video on the internet showing chaotic scenes at what they said was a field hospital filled with wounded fighters and civilians trapped in the town.
On Monday morning, the Sana state news agency reported that army units had "restored security and stability" to most districts of Qusair, and "eliminated large numbers of terrorists, most of them non-Syrians". Twelve leading rebels allegedly among the dead were named.
However, state television's reports from the Qusair area were all filmed from well outside the town's perimeter and gave no sense that it had fallen almost entirely to the government forces, says the BBC's Jim Muir in Beirut.
Activist groups also denied that the army had captured most of the town. One report said that six army tanks were destroyed as they tried to advance.
Our correspondent says it is not clear how many civilians remain trapped in Qusair.
Opposition sources estimate that at least 40,000 are still there, though it is thought many may have fled long ago, he adds.
State television said that the army had set up a protected corridor for civilians to escape the fighting, but activists said many people feared persecution and torture once they entered government-controlled areas.
The main opposition alliance, the National Coalition, warned of an impending "massacre", and called for an emergency meeting of the Arab League.
There were also reports that members of the Lebanese Shia Islamist movement, Hezbollah, had joined the government side in the battle, while Lebanese Sunni militants were said to be supporting the rebels.
The Syrian Observatory for Human Rights, a UK-based activist group, said 23 elite Hezbollah fighters had been killed and about 70 wounded.
Several mortar rounds fired from Syria also struck Lebanon's north-eastern town of Hermel - a Hezbollah stronghold - on Sunday, Lebanon's National News Agency said. No casualties were reported.
Refugee health risks
In a separate development on Monday, Oxfam said Jordan and Lebanon were in urgent need of help to support hundreds of thousands of Syrian refugees who have fled the fighting.
A combination of rising summer temperatures and poor sanitation posed increased health risks for the refugees, the British aid agency warned.
Many of those crossing the border from Syria end up in inadequate shelters, it added. Some refugees are living in an empty shopping centre; others on the outskirts of a cemetery.
The UN says more than 1.5 million Syrians have fled abroad. There are also an estimated 4.25 million internally displaced people.
Meanwhile, Russian Foreign Minister Sergei Lavrov has warned against setting arbitrary deadlines for the international conference proposed by Washington and Moscow to find a political solution to the conflict.
"Some our partners, and [US Secretary of State] John Kerry mentioned that a couple of days or a week should be enough," he told the government daily, Rossiskaya Gazeta.
"Previous peace conferences have lasted months, even years," he added. "I don't want it to be the same with Syria. But it's absolutely counterproductive to set artificial time restrictions."
He also stressed the need to invite Iran, President Assad's strongest ally.
The UN says more than 80,000 people have been killed since the anti-government protests erupted in March 2011.