Taliban kidnappers killed one of their 23 South Koreans hostages and will kill the rest if their demands are not met by 8.30pm this evening, a Taliban spokesman said.
A local government official confirmed the death.
"Yes, they have killed one of the hostages and efforts are underway to have the others released," district chief of Qarabagh district of Ghazni province, Khowja Seddiqi, said.
The Taliban had complained the Afghan government had failed to release any Taliban prisoners as the kidnappers had demanded and as, according to the rebel spokesman, Korean negotiators had assured them Kabul would do.
"Since Kabul's administration did not listen to our demand and did not free our prisoners, the Taliban shot dead a male Korean hostage," Qari Mohammad Yousuf said.
"If the administration of Kabul is not ready to release our hostages, then by 1 am (local time) the rest of the hostages will be killed," he said. "That time is the last deadline."
He said the Korean hostage had been killed in a desert area in the Qarabagh district of Ghazni close to where the 23 Korean church volunteers - 18 women and five men - were abducted on the main road south from Kabul last week.
He rejected Korean media reports that said the Taliban planned to free eight of the captives.
Afghan President Hamid Karzai has pledged not to swap prisoners for hostages after being heavily criticised at home and abroad for releasing five Taliban from jail in March in exchange for an Italian reporter.
But the president and ministers have remained silent throughout the latest hostage ordeal.