Two Western journalists were more than a dozen people killed on Wednesday as Syrian forces pounded the rebel city of Homs, activists said, while calls mounted for a truce to allow in humanitarian aid.

The latest barrage came a day after security forces killed at least 68 people across Syria, adding to an overall death toll of 7,636 since March when anti-regime protests broke out, the Syrian Observatory for Human Rights said.

The toll includes 5,542 civilians, the head of the Britain-based rights monitoring group, Rami Abdel Rahman said.

At least 13 more civilians were killed in shelling of the Baba Amr district of Homs early on Wednesday, the 19th straight day that the city in central Syria was being pounded, the Observatory said.

American journalist Marie Colvin, who reported for London's Sunday Times and French freelance photojournalist Remi Ochlik were killed in the bombing of Baba Amr, French Culture Minister Frederic Mitterrand said.

France's President Nicolas Sarkozy said the deaths of the journalists showed that 'this regime must go.'

Activist Omar Shaker from inside Baba Amr said that two were killed and three others wounded as a shell crashed into a makeshift media centre set up by anti-regime militants.

The French newspaper Le Figaro said one of its reporters, Edith Bouvier, was wounded in the legs.

The area remained the target of random shelling, blocking attempts to remove the bodies, Shaker said.

French television reporter Gilles Jacquier was killed in Homs last month as a shell exploded amid a group of journalists covering protests in the city on a visit organised by the Syrian authorities.

A Syrian citizen journalist, Rami al-Sayyed, who provided live footage on the Internet from Baba Amr, was killed late Tuesday when a rocket hit a car in which he was travelling, activist Hadi Abdullah told AFP.

Despite a plea by activists to allow women and children to flee Homs's besieged Baba Amr neighbourhood, more troops were sent on Tuesday to the outskirts of the restive city, monitors and activists said.

A call by the International Committee for the Red Cross (ICRC) for a two-hour truce daily to deliver aid to afflicted areas has gained support from the United Nations, as well as from the United States and Russia.

Tuesday's call came a day after the ICRC said it was in talks with Syrian authorities and rebels to halt the violence.

Syria's main opposition group, meanwhile, demanded the international community create 'safe havens' in the country and called on Russia to force the regime to allow access for humanitarian convoys.

At a news conference in Paris, the Syrian National Council said it would attend a summit of the countries known as the 'Friends of Syria' and ask for safe zones to protect civilians and allow the opposition to organise.

The rebel Free Syrian Army head, Colonel Riyadh al-Asaad, has welcomed the humanitarian truce call but voiced doubts that the 'criminal' regime would abide by a ceasefire arrangement.

And the UN under secretary general for humanitarian affairs, Valerie Amos, called on Syria to allow aid groups unimpeded access to the country.

"This is a major human rights crisis that is now moving into significant humanitarian consequences," Amos said.

In Washington, White House press secretary Jay Carney said "We support calls for ceasefires to allow for the provision of humanitarian supplies to Syrians who desperately need it."

"Reprehensible actions taken by the Assad regime have led us to a situation where basic supplies, humanitarian supplies are very scarce."

Moscow, a staunch ally of the Syrian-regime, on Wednesday also supported the ICRC call for a truce, expressing 'serious concern' about the humanitarian situation, according to foreign ministry spokesman Alexander Lukashevich.

And although top US military officer, General Martin Dempsey, has said it was "premature" to arm Syria's opposition, top Republican Senator John McCain renewed his call for the outgunned rebels to be supplied with weapons.

But State Department spokeswoman Victoria Nuland said "From our perspective, we don't believe that it makes sense to contribute now to the further militarisation of Syria."

"What we don't want to see is the spiral of violence increase. That said, if we can't get Assad to yield to the pressure that we are all bringing to bear, we may have to consider additional measures," she said.

US Secretary of State Hillary Clinton said Syria was increasingly under pressure.

The Friends of Syria meeting in Tunis on Friday will "demonstrate that Assad's regime is increasingly isolated and that the brave Syrian people need our support and solidarity," she said.

Clinton is to take part in the meeting, the State Department said.

Russia announced that it would not attend because it was being convened "for the purpose of supporting one side against another in an internal conflict," the foreign ministry said.

The Friends of Syria group will meet for the first time after being created in response to a joint veto by China and Russia of a UN Security Council resolution condemning the bloody crackdown.