LONDON, England (CNN) -- A body delivered to British authorities in Iraq is that of British hostage Alec MacLachlan, the prime minister's office said Thursday.
"My thoughts and, I believe, the thoughts of the whole country are with the MacLachlan family at this time of great grief. No family should have to endure what they have gone through," Prime Minister Gordon Brown said.
MacLachlan was one of five British men seized more than two years ago in Baghdad, along with Alec McMenemy, Jason Creswell, Jason Swindlehurst and Peter Moore.
The bodies of Creswell and Swindlehurst were handed over in June, and Brown said in July that he believed MacLachlan and McMenemy were dead.
He said Thursday he hopes the fifth man, Peter Moore, is still alive.
"We are demanding of the hostage takers that they now give us information about the whereabouts of Alan McMenemy and return Peter Moore, who we still believe to be alive, as soon as possible," Brown said.
"We will pursue these hostage takers. There is no justification for what they've done," he said.
Moore is a computer expert. The other four men were security guards.
The five men were kidnapped from the Iraqi finance ministry in Baghdad in May 2007 by people posing as security forces and government workers on official business.
CNN has not confirmed if McMenemy and Moore are dead or alive.
The guards worked for Canadian-based security firm GardaWorld, according to the company. Moore worked for U.S.-based BearingPoint.
At least three videos have been released by the kidnappers, a little known-group calling itself The Islamic Shiite Resistance of Iraq.
In December 2007, the Arabic language TV station al-Arabiya showed a video of a man who identified himself as "Jason." He says on tape that the date is November 18.
The hostage-takers demanded in the video that all British troops be withdrawn from Iraq within 10 days or they would "kill the hostage... as an initial warning."
In February 2008, Peter Moore appeared in a second video, pleading with the British government to perform "a simple exchange" of prisoners with his captors so "we can go home."
"It's a simple exchange -- release those that they want so we can go home. It's as simple as that. It is a simple exchange of people. This is all they want, just have their people released," he said.
The British Embassy in Iraq received a third video in March of this year but refused to disclose its contents.
There has been action recently on a number of long-running detentions in Iraq.
Five Iranians held in Iraq by the United States since 2007 went back to Tehran July 12, Iran's government-backed Press TV reported.
Three of the men said they were diplomats, but the U.S. military said they were thought to be connected to Iran's Islamic Revolutionary Guard Corps Quds Force, a group believed to be providing funds, weapons, roadside bomb technology and insurgent training.
They were seized in Irbil, a city in Iraq's Kurdish region, on January 11, 2007. Two were freed in November 2007.
It is not clear who the other two men released in July are.
Their release came about two weeks after the bodies of Creswell and Swindlehurst were recovered.
The British government denies any connection between the two events, insisting there were no negotiations or exchange.
CNN's Ashleigh Nghiem contributed to this report.