Britain is coming under pressure to secure the release of three hostages in Iraq as tributes were paid to two fellow captives whose remains were handed over. Security officers Jason Creswell and Jason Swindlehurst were among a group of five men taken hostage in Baghdad in 2007. But the fate of the three others - IT consultant Peter Moore, from Lincoln, and two other guards named only as Alan, from Scotland, and Alec, from South Wales - is still unknown. Prime Minister Gordon Brown sent his condolences to Mr Creswell's and Mr Swindlehurst's families who he said had received "the worst possible news after two years of very anxious waiting". Sources said the tests on the remains showed they had not been mutilated - but warned it could take British scientists several days to discover exactly how they died. Speaking at Downing Street, Mr Brown called for the three other hostages to be released immediately and said there was "no justification" for hostage-taking. Mr Brown said he had contacted the Iraqi prime minister and was working to secure the men's release "as soon as possible". The remains of Mr Creswell, originally from Glasgow, and Mr Swindlehurst, from Skelmersdale, Lancashire, were handed over to authorities in Baghdad late on Friday. Amid claims the handover could have been a conciliatory gesture, a spokesman for GardaWorld, the Canadian security company which employed the pair, insisted the company was doing everything in its powers to ensure the remaining three captives were released. A spokesman for the firm said Mr Creswell and Mr Swindlehurst were "outstanding individuals and experts". He added: "We continue to be deeply concerned for the remaining three hostages and are doing everything we can to achieve their release." A Foreign Office spokeswoman said they had informed the families "with deep regret". The five contractors were seized on May 29, 2007, by about 40 armed men wearing police uniforms at the Iraqi Finance Ministry. Captain Doug Beattie, who recently retired from service with the Royal Irish Regiment, said the bodies were a "signal" to the British Government and the security company which employed the two dead captives. The evidence would suggest "deep, deep negotiations" are ongoing behind the scenes, Mr Beattie, who served in Iraq and was later decorated for bravery in Afghanistan, added. Mr Miliband described the developments as "distressing" and said the British authorities had worked with the Iraqi authorities with the hope that the men would be released alive and well. Shadow foreign secretary William Hague said: "This is deeply sad and distressing news, in particular for the families who have been waiting so long to know what has happened to their loved ones. "We must still not give up hope for some of the hostages, or relax the constant efforts to bring them home."