Syrian forces raided the hotbed city of Banias on Saturday and killed at least three protesters, activists said as President Bashar al-Assad's opponents proposed he offer elections to end the crisis.

Activists spoke of dozens of tanks and armoured vehicles entering Banias, on the northwestern Mediterranean coast, from three directions as electricity and communications were cut. Tanks also encircled the nearby town of Baida.

The rights activists said residents of Banias formed human chains in a desperate bid to halt the military operation when it began around dawn.

Heavy gunfire was heard in Banias's south, a seaside sector of the city where most of the protesters live, while navy boats patrolled offshore, the activists said, reached by telephone from Nicosia.

A human rights activist said later security forces killed three women who were among around 150 people demonstrating on a road outside Banias on Saturday calling for the release of people who had been arrested.

"Members of the security forces asked them to leave and, when they refused to do so, they opened fire killing three of them and wounding five others who were hospitalised," the activist said.

The military confirmed it conducted an operation in Banias.

"Army units and security forces today pursued members of terrorist groups in and around Banias and neighbourhoods of (the southern flashpoint town of) Daraa to restore security and stability," said the military official.

"They arrested people and seized a quantity of weapons that these groups have used to attack the army and citizens and scare people."

An Internet-based Syrian opposition group, meanwhile, proposed that Syria's embattled president offer to hold elections in six months in order to bring to an end the crisis that has engulfed his country for more than seven weeks.

The Syrian Revolution 2011, a Facebook group that has been a motor of the protests, urged Assad to 'stop shooting at demonstrators, allow peaceful demonstrations... release all political prisoners, allow political pluralism and free elections in six months'.

In a statement posted online, it told Assad he could be the 'pride of contemporary Syria' if he transformed Syria 'from a dictatorship to a democracy'.

"The Syrians will be grateful and it is possible to do."

The group had called for Friday's 'Day of Defiance' demonstrations, which saw tens of thousands of people take to the streets in Syria calling for democratic reforms.

Rights groups said 26 protesters were shot dead by security forces on Friday while the military said 10 soldiers and policemen were killed in Homs by 'armed terrorist groups'.

Residents had expected the army to attack after reporting seeing earlier this week dozens of armoured vehicles, including tanks and troops reinforcements, deployed on the outskirts of the coastal city.

"It looks like they are preparing to attack the town, like they did in Daraa," one activist said.

On Thursday, a convoy of 40 military vehicles pulled out of Daraa, another protest centre, which the military had locked down since April 25.

Dozens of people were killed during the 10-day military assault on Daraa, launched with what activists termed 'indiscriminate' shelling of the town.

But General Riad Haddad, the military's political department chief, insisted troops in Daraa 'did not confront the protesters'.

"We continue searching for terrorists hidden in several places. As the army, we never confronted the protesters," he said.

Human rights groups say that more than 600 people have been killed and 8,000 jailed or gone missing in the crackdown on protesters since demonstrations erupted in mid-March.

The Committee of the Martyrs of the 15 March Revolution, which has been keeping a tally of the dead, puts the death toll at 708.

The United States warned it would take 'additional steps' against Syria if it continues its brutal crackdown on protesters, a week after imposing tough sanctions on the Arab nation.

It also welcomed the European Union's decision to impose sanctions on Syrian officials 'responsible for human rights abuses'.

The EU on Friday agreed to impose sanctions on 13 Syrian officials involved in the regime's brutal crackdown on protests and will meet on Monday to discuss whether to target Assad as well, diplomats said.

Human Rights Watch meanwhile called on the UN General Assembly to strongly reject Syria's candidacy for the UN Human Rights Council.

"Syria's candidacy is an affront to all those facing its brutal repression, and to human rights supporters everywhere, and should be decisively rejected," said Peggy Hicks, global advocacy director at HRW.

New members to the UN Human Rights Council are to be elected on May 20 and Syria is one of the candidates.