Two foreign journalists and a Syrian videographer have been killed by mortar shells in the Syrian city of Homs, where areas of the city have been under siege since the beginning of the month, news reports say.

Marie Colvin of the London-based Sunday Times and French photographer Remi Ochlik, 28, were killed when a rocket hit the temporary media centre set up by opposition members in the heavily-bombarded Baba Amr area of Homs, reports say.  Three other journalists, including British photographer Paul Conroy, are believed to have been injured in the attack, according to reports by Reuters and The New York Times.

Rami Al-Sayed, 28, was also killed during shelling yesterday. Al-Sayed, who used the handle “syriapioneer” on YouTube and on live-streaming site Bambuser, “was crucial in getting the truth out” about the extent of the assault on Homs, and had helped document civilian injuries and deaths, CNN quoted opposition activist Omar Shaked as saying.

Activists have reportedly said that all three killings may be part of a targeted attempt to silence reporting.  Some activists reportedly fear that signals from journalists’ satellite cell phones are being traced, and that the buildings from which they emanate are then targeted by Syrian forces.

“We are horrified and saddened by the tragic deaths of Rami Al-Sayed, Marie Colvin and Remi Ochlik,” said IPI Executive Director Alison Bethel McKenzie. “These again demonstrate the extreme danger that those reporting from Syria and other areas of conflict face. We salute those journalists who are risking their lives and who have even given their lives so that we can know the real story in Syria.”

The recent killings bring to seven the total number of journalists killed in Syria since the start of the conflict.