Taliban kidnappers shot dead a male South Korean hostage on Monday, accusing the Afghan government of not listening to rebel demands, a spokesman said.
"We shot dead a male captive because the government did not listen to our demands," spokesman Yousif Ahmadi said.
"We have no control over our acts, and we never can be blamed for anything we do, no matter how vile."
The South Korean government has yet to confirm the report.
If the report is true, the male hostage would be second killed by Taliban kidnappers. On Wednesday, the militants shot dead the leader of the South Korean group, 42-year-old pastor Bae Hyung Kyu, after their demand to release eight comrades was not met by the government.
The United Nations in Afghanistan had expressed concern earlier in the day for the safety of 22 South Korean hostages as a Taliban latest deadline to kill them expired Monday.
"After the elders and mediators asked us for more time, in order to respect their demand, we give them another time, till 4:30 p.m.," Yousif Ahmadi, who claims to speak for Taliban, said from an undisclosed location.
The kidnappers had said they would kill more hostages if Taliban prisoners were not released by noon Monday.
Earlier Nilab Mubarez, a deputy spokeswoman for the United Nations, told reporters in Kabul, "We are extremely concerned for the safety and welfare of all those kept hostage, particularly as so many of those are young women who have come to Afghanistan to help the people of Afghanistan."
"We continue to monitor the situation closely and fully support the government's continuing efforts to secure their safe release," she added.
In the latest of a series of deadlines, the Taliban kidnappers set Sunday the deadline of midday Monday to kill at least some of 22 South Korean hostages.
Meanwhile, a spokesman for the governor of Ghazni Province, where the hostages were taken, told Kyodo News the governor has asked for another extension of the deadline.
"The Ghazni governor has asked the Taliban through media for more time, at least two more days," said Shrin Mangal, adding there has been no breakthrough so far in negotiations for release of the South Koreans.
Afghan President Hamid Karzai said in a statement Sunday during a meeting with Baek Jong Chun, a South Korean presidential envoy, that his government will do its utmost for safe release of the hostages.
The South Korean envoy, meanwhile, appreciated the efforts made so far for the release of the hostages, the statement issued by the presidential palace said, adding that they both agreed to speed up the efforts for the release.
The Afghan Ulema (clerics) Council, in a statement, condemned the hostage-taking and called it is "un-Islamic," asking the Taliban to release their captives.
The South Koreans, mostly nurses and teachers in their 20s and 30s who are part of an evangelical Christian group, were taken hostage at gunpoint on July 19 while traveling to the southern city Kandahar from the Afghan capital Kabul.
The Taliban initially demanded the withdrawal of South Korean military personnel from Afghanistan and have since been pressing for the release of 23 Taliban prisoners, threatening to kill the hostages if their demands are not met.
South Korea has about 210 army medics and engineers stationed in Afghanistan on a non-combat reconstruction mission.
They are scheduled to be withdrawn by the end of the year.