South Korea's foreign minister has appealed for the release of a Korean man threatened with execution by Islamic militants in Iraq.
The deadline expired at sunset on Monday
Foreign Minister Ban Ki-moon said South Korea was a friend of Iraq, and urged the release translator Kim Sun-il, 33.
There has been no news since the expiry of a deadline set by the kidnappers who said they would kill Mr Kim if Korean troops were not withdrawn by sunset.
Seoul said it would not be deterred from its plans for troop deployment.
Mr Kim's family have pleaded with the government to rethink its policy.
In other developments:
- Senior coalition spokesman Brig Gen Mark Kimmitt said a weekend air strike in Falluja killed key figures in suspected leading militant Abu Musab al-Zarqawi's network; local residents said civilians were killed in the attack
- The bodies of four US soldiers have been found in Ramadi, west of Baghdad; it is unclear when they died
- Iraq has begun exporting oil from its two southern terminals again after they were attacked by saboteurs last week
- Radical Shia cleric Moqtada Sadr has been invited to take part in next month's Iraqi national conference
Speaking at an Asian ministerial conference in China, Ban Ki-moon said South Korea was doing all it could diplomatically to free Mr Kim.
A team of diplomats has been sent to Jordan to help in the negotiations, and Arab ambassadors in Seoul have been asked for their help.
Mr Ban said South Korea's decision to send 3,000 troops was to help in the rehabilitation of the country.
"We regard [ourselves as]... friends of the Iraqi people and there should be no cause for anyone to have kidnapped our national," he said.
"We really urge and appeal to those responsible in this case to release immediately and unconditionally and safely our national kidnapped."
In the video released by the militants on Sunday, Kim Sun-il screams:
"Korean soldiers, please get out of here. I don't want to die. My life is important"
The video was broadcast on the Arabic TV channel al-Jazeera, which said that it had arrived in an unmarked package at the station's Baghdad office.
The two-minute tape showed the hostage surrounded by armed men wearing masks.
"We ask you to withdraw your forces from our land and not to send any more troops, and if not we'll send you this Korean's head," said one of the men.
The tape said that the 24-hour deadline would expire at sunset (2015 local time, 1615 GMT) on Monday.
A banner identified the group as Jamaat al-Tawhid and Jihad, which is led by a leading al-Qaeda member, Abu Musab al-Zarqawi.
Last month, the same group beheaded an American hostage, Nick Berg, and it has been responsible for a number of other attacks, including the killing of Iraqi Governing Council head Ezzedine Salim.
South Korea already has 660 army engineers and medical personnel in the southern Iraqi city of Nasiriya, where they are involved in humanitarian and rehabilitation projects.
On Friday, the South Korean defence ministry announced it would send another 3,000 troops to northern Iraq from early August.
The next day, the government issued a warning against any travel to Iraq, saying its troop decision might lead to attacks on South Korean citizens.
There has been considerable opposition in South Korea to the deployment of troops in Iraq.
The BBC's Charles Scanlon in Seoul said that opposition could now grow following Mr Kim's capture.
On Monday night, hundreds of protesters held a candlelit vigil in Seoul demanding Mr Kim's release and a reversal of the decision to despatch South Korean troops.
Kim Sun-il is reported to have been abducted on 17 June in the city of Falluja, one day before South Korea announced its increased troop deployment.
South Korean officials said that his employer, Gana Trading Company - a supplier to US troops in Iraq - had already tried to negotiate Mr Kim's release without informing the government of the situation.
The company has 12 staff in the Iraqi capital and the other employees have been moved to a hotel.
The firm told Yonhap news agency that militants were holding 10 other foreigners, including a European journalist and some people working for America.