Western powers condemned Syria for the killing of two foreign journalists, with Washington slamming the regime's "shameless brutality'' and Paris holding Syrian authorities responsible.
US war correspondent Marie Colvin of Britain's Sunday Times and French freelance photojournalist Remi Ochlik were killed in the city of Homs in what activists said was shelling by President Bashar al-Assad's forces.
Three other Western journalists were wounded in the attack on a makeshift media centre in the Baba Amr district, including Colvin's British photographer colleague Paul Conroy and French reporter Edith Bouvier of Le Figaro.
"This tragic incident is another example of the shameless brutality of the Assad regime,'' US State Department spokeswoman Victoria Nuland told AFP.
France demanded access to the victims of the attack and summoned Syria's envoy to Paris, "to remind him of the intolerable nature of the Syrian government's behaviour,'' Foreign Minister Alain Juppe said in a statement.
He added that the Syrian government must immediately stop the attacks.
"Damascus owes us an answer,'' Juppe said. "France holds the Syrian authorities responsible and accountable for the deaths of the journalists.''
In Washington, US State Department spokeswoman Victoria Nuland condemned the "tragic incident'' as another example of the "shameless brutality'' of the Assad regime.
White House spokesman Jay Carney said the "brutality of the Assad regime becomes ever more apparent each day.''
French President Nicolas Sarkozy said the incident was a further sign that Assad should give up power.
"This shows that enough is enough, this regime must go. There is no reason why Syrians should not have the right to live their lives, to freely choose their destiny,'' Sarkozy said.
British Prime Minister David Cameron paid tribute to Colvin, saying her death in Syria showed the risks journalists face in exposing the truth.
"This is a desperately sad reminder of the risks that journalists take to inform the world of what is happening and the dreadful events in Syria,'' Cameron told parliament.
Britain summoned the Syrian ambassador to the foreign ministry to lodge a protest over the deaths.
"Governments around the world have the responsibility... to redouble our efforts to stop the Assad regime's despicable campaign of terror in Syria,'' Foreign Secretary William Hague said.
Russia, which has opposed Western efforts to rein in the Syrian regime, also condemned the deaths.
The foreign ministry said "Moscow resolutely condemns and is seriously concerned'' by the killings.
"This tragic event once again confirms the need for all the sides of the Syrian conflict to end the violence and move toward a political course with the start of an all-encompassing national dialogue without preconditions.''
European Union foreign policy chief Catherine Ashton described the killings as criminal.
"The escalation of violence in the country must be immediately brought to an end,'' Ashton's office said in a statement.
Syrian authorities insisted they were not aware Colvin and Ochlik had entered the country and urged foreign reporters in Syria to register with the government.
"The authorities had no information that the two journalists had entered Syrian territory,'' Information Minister Adnan Mahmud told AFP.
Mahmud said he had asked "specialised authorities in Homs to look for them (Colvin and Ochlik)''.
"The ministry urges all foreign journalists who entered Syria illegally to report to the nearest immigration office to legalise their presence,'' he added.
US-based media tycoon and Sunday Times owner Rupert Murdoch hailed Colvin as one of the best foreign correspondents of her generation.
"Our photographer, Paul Conroy, was with her and is believed to have been injured. We are doing all we can in the face of shelling and sniper fire to get him to safety and to recover Marie's body,'' Murdoch said in a staff email.
Murdoch said Colvin, who was 56, had fearlessly covered conflicts for The Sunday Times for 25 years.
Ochlik, who was 28, was in Syria taking pictures for the IP3 Press agency, which he co-founded in 2005 and for which he had covered previous conflicts including the Arab Spring revolts in Tunisia and Egypt and the conflict in Libya.
The Committee to Protect Journalists condemned the killings.
"The killing of these journalists, who were observers in a conflict zone, represents an unacceptable escalation in the price that local and international journalists are being forced to pay,'' CPJ deputy director Robert Mahoney said in a statement.