Syria: Army 'moves on Jisr al-Shughour'
The Syrian army has moved against the town of Jisr al-Shughour where the government says 120 security personnel were killed earlier this week.
Heavy gunfire has been reported in the area. The expected action has prompted a flow of refugees to nearby Turkey.
Elsewhere in Syria, anti-government activists say at least 22 people have been killed by security forces.
Tanks are also reported to have shelled Maarat al-Numan in the north with "dozens" killed or wounded.
State TV said police stations in the town had been attacked by gunmen.
Turkey says more than 2,000 Syrians have crossed the border seeking refuge from the anticipated crackdown in Jisr al-Shughour.
Turkish PM Recep Tayyip Erdogan has said Syria is committing "atrocities", in remarks quoted by Turkish media.
Syria's government has blamed the deaths in the town on armed groups, but there are reports of a mutiny among security forces.
Syrian state TV said armed men had prepared defences and set fire to crops and trees around Jisr al-Shughour in order to slow the army's advance.
Activist websites have carried reports from people in the area saying there was heavy gunfire in a village where barricades of burning tyres had been set up to block the road to the town.
Syria has prevented foreign journalists, including those from the BBC, from entering the country, making it difficult to verify reports from there.
In other developments:
- Activists say at least 11 protesters were killed to the east of Idlib town, in Idlib province where Jisr al-Shughour is located
- Two protesters were shot dead in the Busra al-Harir area of southern Deraa province, activists say
- Opposition groups say four more protesters were shot dead in the Qaboun district of the capital, Damascus
- Five demonstrators was shot dead during protests in Latakia, according to activists
- Eyewitnesses in the central city of Hama tell BBC Arabic that thousands of protesters gathered in al-Aassi Square, the main square in the city centre - there is no security or police presence at all
- There are protests in the cities of Homs, Hasska, al-Qamishili and al-Amood. Gunfire has been heard in Bab Amr, a suburb of Homs
The BBC's Jim Muir, in Beirut, Lebanon, says the events in Jisr al-Shughour present a massive challenge to President Assad.
Syrian state TV has been preparing for the security operation in the town by widely broadcasting the movement of troops in the area, prompting many residents to flee.
The action against Jisr al-Shughour is in response to claims by Damascus that armed gangs killed 120 members of the security forces there after protests against President Assad's rule.
State TV has been broadcasting images of what it says are soldiers and police shot dead in the town.
The government says local residents requested the army's intervention to restore peace and quiet.
But dissenting accounts say the violence was sparked by deserting soldiers, and that loyal troops have massacred peaceful civilians.
Human rights groups say more than 1,100 people have been killed since protests against President Assad began in March, and it now appears several hundred security forces may also have died.
Turkey's Prime Minister Erdogan has previously been reluctant to criticise Syria, but in an interview quoted by Anatolia news agency, he said the Assad regime was committing "atrocities" against anti-government demonstrators.
"They are not acting in a humane manner. This is savagery," he said in a TV interview on Thursday.
The unrest in Syria has prompted a split within the UN Security Council, where France and Britain have proposed a resolution to condemn the government's actions.
But other nations on the council, including Brazil, China and Russia, say such a resolution - which does not propose concrete action - could further inflame tensions in an already volatile region.
The UN human rights chief, Navi Pillay, and the Pope have urged Damascus to show restraint, with Ms Pillay strongly condemning the Syrian government.
The Syrian army has moved against other cities that have seen anti-government protests, including Deraa, Baniyas, Rastan, Latakia, Homs, Hama and some Damascus suburbs.
Anti-government activists have promised to mount widespread protests after Friday prayers.
One Facebook page was billing it a "Day of Tribes", in an attempt to draw in more of Syria's powerful tribes to the protests, says our correspondent in Beirut.
The Red Crescent has set up a tent city to house Syrian refugees across the border in the Turkish town of Yayladagi and there are plans to set up a second camp in Altinozu.
A Turkish official told the BBC the influx of Syrians was sharply increasing and the latest arrivals included several dozen wounded people.
Most of the refugees were too frightened to speak to the BBC's Owen Bennett-Jones, who is in Yayladagi.
But one man, who spoke on condition of anonymity, said he had made a three-hour trek from Jisr al-Shughour, dodging Syrian soldiers along the way.
He said an estimated 30,000 Syrian soldiers were massing near the town - but added that hundreds of soldiers had also deserted and were also gathering on the border hoping to make an escape into Turkey.
A Syrian government spokeswoman said there were no refugees fleeing to Turkey, just the normal traffic of people visiting relatives across the border.