Hundreds of thousands of protesters flooded cities around Syria on Friday in what activists described as the largest outpouring yet against the regime of President Bashar Assad and a powerful message of the opposition's resolve.

At least 14 people were killed in various clashes, activists said, though one human rights campaigner estimated the death toll at 24.

The wildfire rage — flaring in dozens of places at the same time — further strained the resources of Assad's security forces and military as they also try to choke off a refugee wave into Turkey.

The centrepiece of the latest protests — the central city of Hama — brings further complications for the government. Security forces moved outside Hama in early June after shootings that left 65 people dead, and now the streets appear fully under the sway of the opposition with an estimated 300,000 people gathering Friday in the central square, activists said.

Crowd estimates and other details cannot be independently verified. The Syrian government has banned most foreign media from the country and restricted coverage.

But the protest surge Friday appeared to dwarf recent weeks as Assad's forces tried to wear down the opposition with relentless force. Syrian rights groups say more than 1,400 people have been killed, most of them unarmed protesters, since mid-March.

The regime disputes the toll, blaming "armed thugs" and foreign conspirators for the unrest that has posed the most serious challenge to the Assad family's 40-year ruling dynasty in Syria.

Refugee clampdown

In Hama, anti-government crowds defiantly staked their claim to the city. Syria-based activist Mustafa Osso estimated 300,000 people joined the rally in Hama without any sign of security forces, which remained outside the city and appeared unwilling to risk major bloodshed again.

Those forces are increasingly mobilized in difficult terrain along the Turkish border in efforts to clamp down on refugees fleeing across the border. The regime is deeply embarrassed by the exodus and also fears the camps could become opposition enclaves out of the government's reach. More than 10,000 Syrians have already taken shelter in refugee camps in Turkey to escape the violence.

"Syrian security forces are exhausted," Osso said. "There are demonstrations all over Syria and they cannot cover these areas."

Human rights lawyer Razan Zaitouna told the Reuters news agency that 24 civilians were killed in Friday's protests.

Omar Idilbi, a spokesman for the Local Coordination Committees, which track the protests in Syria, said Friday's demonstrations were the largest since the uprising began in mid-March. He did not give a figure, but said there were gatherings in 172 different locations with numbers ranging from few hundreds to hundreds of thousands as in Hama.

State-run Syrian TV aired footage of pro-government demonstrators in different parts of the country carrying Syrian flags and posters of Assad. State TV said gunmen opened fire at police officers, killing a police officers and a civilian.