There are fears the journalist, who ran the Homs media centre and helped photographer Paul Conroy escape the city, has been subject to torture and mistreatment after being seized by the authorities.
The Foreign Secretary William Hague has led calls for the Syrian government to release Syrian activist journalist Ali Mahmoud Othman, saying he was concerned to hear reports that he had already been tortured and maltreated.
In a statement, he said: “I call on the Syrian authorities to release Mr Othman and other political prisoners immediately. The Syrian regime will be held responsible for Mr Othman’s safety and his treatment and I will raise his case in Istanbul at the Friends of Syria meeting tomorrow.
“It is believed that up to 10,000 Syrians have been killed by the regime since the start of the crisis, with many more incarcerated, as part of the regime’s campaign of terror.”
Ali saved the lives of many journalists including Colvin’s photographer, Paul Conroy.
A fellow Syrian activist told CNN: “We believe Ali is being subjected to severe torture. The lives of our activists and citizen journalists across the whole country are now at risk.”