"The German national and four Afghans we had reported to have killed are still alive," Qari Mohammad Yousuf, told Reuters from an unknown location by telephone.

In exchange for the hostages' release, Yousuf said the Taliban demanded the release of 10 prisoners held by the Afghan government and the withdrawal of Germany's 3,000 troops stationed in Afghanistan.

Other news agencies reported similar statements and demands from Taliban leaders on Monday.

The body of a second German found over the weekend was returned to Germany for an autopsy on Monday. It remained unclear whether the man, identified as Rüdiger B., died of gunshot wounds or if his captors shot his body after his death. The German government has said he was not executed.

Crisis team still at work

In Berlin, Chancellor Angela Merkel said on Sunday in a television interview that Germany would not allow itself to be blackmailed by the Taliban.

"We are not going to respond to demands from the area of the Taliban," Merkel told the ARD public television. "We cannot be blackmailed."

She said she had "no new reliable information" regarding how the hostage died or on the whereabouts of the other man. Berlin has set up a crisis team to evaluate all information regarding the pair of Germans kidnapped last week. The two men were reported to be engineers working on a dam project south of Kabul.

Though it is not a position shared by any of Germany's main political parties, a recent survey showed that some 60 percent of Germans support pulling Bundeswehr troops out of Afghanistan. This autumn, the German parliament is scheduled to debate whether to extend the three mandates governing the army's deployment to Afghanistan.

South Koreans' ultimatum extended

Taliban rebels also extended the deadline on Monday for their demands to be met before killing 23 South Korean hostages seized Thursday. It's the second 24-hour extension the militants have given the South Korean government.

"Since the Afghan government has not sincerely tried to solve the problem, this time we are giving another 24 hours to the Korean government to solve the matter Yousuf told the dpa news agency.

Afghan Interior Ministry spokesman Zemarai Bashary said earlier that authorities were "working on the issue constantly, around the clock."

"We have more hope of success for the release of both the South Koreans and the German," he said. "We hope to win their release via talks rather than military operations."

Taliban leaders said the hostages would be killed if the troops mounted a raid to free the prisoners.