Iraqi insurgents have killed a Lebanese man and two Iraqi co-workers, Lebanese officials say.
Three of the captured Turkish men were shown on a tape
The foreign ministry in Beirut said Hussein Ali Alyan, 28, a Shia Muslim construction worker, had been tortured and killed in "grisly circumstances".
His body and those of the two Iraqis were dumped on a road near Baghdad.
In a separate development, seven Turkish contractors were released five days after being taken hostage in the violence-wracked town of Falluja.
Turkish officials said the men were travelling to the northern city of Mosul and would cross the border into Turkey later in the day.
A Turkish diplomat in Baghdad told Reuters news agency the Turks were "in good health".
They were displayed on a video earlier in the week by their kidnappers, who claimed to be from a militant group and called on Turkish firms to end their business in Iraq.
Mr Alyan, from southern Lebanon, was apparently one of three Lebanese nationals working for a telecommunications company who were kidnapped in Iraq.
One was released and a third remains in captivity, according to reports.
Dozens of foreign workers have been taken hostage by Iraqi insurgents in recent months. Some have been killed and others released.
On Tuesday, three Italian hostages and a Polish man were rescued by military special forces.