American correspondent Marie Colvin and French photographer Remi Ochlik were killed in the Syrian city of Homs on Wednesday when rockets fired by government forces hit the house they were staying in, opposition activists and witnesses said.

At least two other journalists and possibly more were wounded in the attack, the Syrian Network for Human Rights said.

One of the wounded was named as British photographer Paul Conroy, the other as Edith Bouvier of France's Le Figaro newspaper. She was said to be in serious condition.

A witness contacted by Reuters from Amman said shells hit the house in the opposition-held Baba Amro district of Homs which was being used as a media centre. A rocket hit them when they tried to escape.

Colvin and Ochlik were both prize-winning veterans of wars in the Middle East, Asia and elsewhere.

The British-based Colvin, who worked for the Sunday Times, lost an eye when she suffered a shrapnel wound while working in Sri Lanka in 2001. In public appearances after that attack, she wore a black eye patch.

Among her awards was a Martha Gelhorn Prize in 2009 for distinguished work over many years

Ochlik was born in France in 1983 and first covered conflict in Haiti at the age of 20. Most recently he photographed the revolutions in Tunisia, Egypt and Libya.

He won first prize for general news in this year's World Press Photo awards for a photo of a rebel fighter in Libya and ran his own agency, IP3 Press.

In Paris, Reporters Without Borders said Bouvier working as a freelancer for Le Figaro newspaper.

Video broadcast from Homs showed the bodies among the rubble.

"We don't know if the building was deliberately targeted... we urge Syrian authorities to stop bombing Homs, said its Middle East director, Soazig Dollet.

Activist Abu Thaer said four journalists were wounded. They were being treated in a makeshift hospital but there was nothing that could be done for them and they needed to be urgently evacuated.

"There is hardly any medical equipment or medicine to treat people," he said on Skype.

The Syrian conflict is especially dangerous for journalists to cover as opposition and rebel forces are for the most part bottled up in enclaves which can only be reached by hazardous journeys.

A Syrian photographer, Rami al-Sayed, died on Tuesday because there was nothing to treat him with, Abu Thaer said.

The Committee to Protect Journalists and Reporters Without Borders have also documented the deaths of at least other four Syrian journalists.

Syria banned almost all foreign journalists from the start of the uprising March 2011, but has started issuing short-term visas for a limited number of journalists, who are allowed to move around accompanied by government minders.

Gilles Jacquier, of the French TV station France 2, was killed in January while on a government-authorized reporting visit to Homs. Last week New York Times reporter Anthony Shadid died of an asthma attack while returning to Turkey from an opposition zone.

Pro-opposition areas of Homs have been under a sustained bombardment from government forces since February 3. Several hundred people have been killed, activists say.

YouTube video from Homs activist Khalied Abu Salah, showed him standing in the rubble next to the bodies of Colvin and Ochlik, on the floor of a grey concrete hallway scarred with bullet marks and cracks from the blasts.

"These are the bodies of the American journalist Marie Colvin and this is the French journalist Remi Ochlik. They are martyrs of the random shelling on the neighborhood of Baba Amro ... There are others injured, among them the journalist Edith who works for Le Figaro."

He raises his fist defiantly and calls for urgent aid to treat the wounded in Baba Amro.

"I am sending a message to the European Union to move immediately. The blood of your own has mixed with Syrian blood. You need to move now," he shouted.-Reuters