Syrian army units stormed into the city of Banias with tanks overnight, attacking Sunni districts that had defied President Bashar al-Assad's autocratic rule, a human rights campaigner said on Saturday.

The units entered the coastal city, a majority of whose residents are Sunni Muslims, from three directions, advancing into Sunni districts but not Alawite neighbourhoods, said the campaigner.

Most communications with Banias have been cut but the campaigner was able to contact some residents, he said.

Assad belongs to the minority Alawite sect, an offshoot of Shi'ite Islam, and Alawites occupy most senior positions in the army and security apparatus.

'Residents are reporting the sound of heavy gunfire and seeing Syrian navy boats off the Banias coast. Sunni and mixed neighbourhoods are totally besieged now,' said the rights campaigner, who did not want to be identified.

A protest leader said earlier this week that Syrian forces and gunmen loyal to Assad had moved on Tuesday into areas of central Banias that had been under the control of pro-democracy demonstrators for weeks.

The coastal city has witnessed some of the most persistent demonstrations since an uprising erupted in the southern city of Deraa seven weeks ago demanding political freedom and an end to corruption.

Mostly Sunni districts of Banias have been under the control of demonstrators since Assad loyalists, known as 'al-shabbiha,' fired at residents from speeding cars on April 10, after a large demonstration that demanded the 'overthrow of the regime.'

Six civilians were killed that day, according to residents and human rights campaigners.

Authorities described Banias as a 'center of Salafist terrorism' and said armed groups had killed soldiers near the city. Civic leaders in Banias issued a statement denying the accusation and saying the authorities were trying to spread fear among the Alawites.

'They are targeting Sunnis. I regret to say that the propaganda that Assad is spreading that the Alawites will not survive if he is toppled is receiving an audience among our Alawite neighbors, although the demonstrations have been for freedom and unity, regardless of sect,' protest leader Anas Shughri said earlier this week.-Reuters