Militants holding a British man hostage in Iraq have repeated a threat to kill him after killing a second fellow captive, Islamist websites report.
Ken Bigley's kidnappers say they want Iraqi women prisoners freed
The reports have not been verified, but the murdered man is thought to be US citizen Jack Hensley.
Mr Hensley was abducted along with Briton Ken Bigley and another American, Eugene Armstrong, in Baghdad last week.
Mr Armstrong was beheaded on Monday by a group believed to be led by al-Qaeda suspect Abu Musab al-Zarqawi.
The kidnappers, claiming to be from the Tawhid and Jihad group, are demanding the release of Iraqi women prisoners.
Prime Minister Tony Blair spoke to Mr Bigley's family at their Liverpool home on Tuesday.
It is understood he told them there were "limitations" to what the government could do to secure his release, the BBC's Norman Smith said.
Mr Bigley's son had urged Mr Blair to help save his father's life, following Mr Armstrong's murder.
Political correspondent Norman Smith said it was understood the prime minister told members of Mr Bigley's family he appreciated no one could comprehend the agony they must be going through.
On BBC News 24 Mr Bigley's son Craig had urged Mr Blair to "meet the demands... two women for two men".
The 33 year old said: "I ask Tony Blair personally to consider the amount of bloodshed already suffered."
But BBC political editor Andrew Marr said there was very little the UK government could do to resolve the situation.
"They can make appeals... but they can't negotiate and they won't negotiate," he said.
He added Mr Blair would not want to say anything that would either provoke the group, or appear to suggest he was prepared to enter into serious negotiations.
"He can't move either way, there's almost nothing he can say at the moment," he said.
A candlelit vigil for Mr Bigley was held on Tuesday night at St Mary's Parish Church in Walton, Liverpool.
A website thought to be linked to the group behind the kidnappings showed video footage of Mr Armstrong being beheaded on Monday.
The nine-minute long tape showed five militants dressed in black behind the sobbing man, blindfolded and wearing an orange jumpsuit.
After reading a statement, the man in the centre, believed to be Mr Zarqawi himself, appeared to pull what looked like a knife and cut the man's throat.
The US later recovered his body.
After killing Mr Armstrong it issued a new 24-hour deadline for the release of all women from US-run Abu Ghraib and Umm Qasr prisons in Iraq
On Tuesday night the website said a film of the second hostage's slaughter would be provided shortly.
The renewed threat to Mr Bigley's life was made later on Tuesday on another website, which has been linked to Mr Zarqawi's group in the past.
The US has said no women are held at either jail, although two female "security prisoners" are held elsewhere.
They include Dr Rihab Rashid Taha, a senior scientist who worked on Saddam Hussein's bacterial weapons programme and was nicknamed Doctor Germ.
UK authorities have said there are no Iraqi women in jails under their control.
The three hostages were kidnapped from the garden of their home in the Mansour district of Baghdad on Thursday.
They had been working for Middle East-based general services and construction contractor Gulf Supplies and Commercial Services.
More than 100 foreigners have been abducted by insurgents in Iraq over the past 17 months.