France called on the Syrian government to immediately halt a military onslaught on the city of Homs and allow safe access for medical aid after two journalists were killed in the opposition hotbed on Wednesday.

American correspondent Marie Colvin and French photographer Remi Ochlik died when rockets fired by government forces hit the house they were staying in, and several other journalists were seriously injured.

Hundreds of people have been killed in more than two weeks of sustained bombardment of Homs, a city of one million, by Assad's besieging forces.

I ask the Syrian government to stop immediately the attacks and respect its humanitarian obligations, French Foreign Minister Alain Juppe said in a statement. (We) have asked our embassy in Damascus to demand from Syrian authorities a securitised passage with medical help to be given to victims with the support of the International Red Cross.

Speaking to reporters on the trail of his re-election campaign, President Nicolas Sarkozy said the journalists' death was an assassination and that Assad's era had to end.

That's enough now, Sarkozy said. This regime must go and there is no reason that Syrians don't have the right to live their lives and choose their destiny freely. If journalists were not there, the massacres would be a lot worse.

France has led Western efforts to try to force Assad to end a crackdown on protests and has suggested a need to set up zones to protect civilians - the first proposal by a major Western power for outside intervention on the ground.

Ochlik, was the second French journalist to die during the Syrian uprising. Gilles Jacquier, of the French TV station France 2, was killed in January while on a government-authorised reporting visit to Homs.

Juppe said that he had summoned Syria's ambassador to condemn the Syrian government's behaviour. France is more determined than ever to end the savage repression that the Syrian people are experiencing every day.

British Foreign Minister William Hague said he was shocked at the death of Colvin, a veteran correspondent for London's Sunday Times, but that his government would not cease its efforts to end Syria's bloodletting.

Governments around the world have the responsibility to act upon that truth - and to redouble our efforts to stop the Assad regime's despicable campaign of terror, Hague said.

Speaking to reporters in Paris, Syrian National Council spokeswoman Basma Kodmani aid the blame firmly on Assad. Homs has become an extremely dangerous place. I don't see any reason for the opposition or revolutionary forces to shoot at journalists. It's most probably people related to the regime.

(Additional reporting by Adrian Croft; Editing by Mark Heinrich)