The Afghan government says it does not believe Taleban claims that the militant group has killed two Germans it abducted near Kabul this week.
The foreign ministry said it believed one hostage had died of a heart attack and the other was still alive.
Earlier, a Taleban spokesman said the two were killed as Germany had ignored a demand to withdraw its 3,000 troops.
The Taleban later renewed a threat to kill up to 23 hostages from South Korea, captured separately on Thursday.
Foreign ministry spokesman Sultan Ahmad Baheen told the BBC the Afghan security forces believed one of the two German engineers kidnapped on Wednesday was still alive.
"We hope that he will be released soon and we are trying our best to get him released," Mr Baheen said.
"The information that we and our security forces have is that one of these two who were kidnapped died of a heart attack."
Local police said the Germans, whose identity has not been revealed, were seized with six Afghan colleagues on Wednesday in Wardak province where they had been working on a dam project.
Germany has about 3,000 troops in the country
German foreign ministry spokesman Martin Jaeger said Berlin was taking the Taleban's statements "very seriously" but had no independent confirmation "that a hostage was murdered in Afghanistan".
Earlier, Taleban spokesman Qari Yousuf Ahmadi said the first hostage had been killed at 1205 local time (0735 GMT) and shortly afterwards that the second German had also been killed.
If confirmed, the killings would be the first of foreign hostages since the death of an Indian engineer in April last year.
Qari Yousuf Ahmadi said the Taleban would start to kill the South Korean hostages if an equal number of militant prisoners were not freed by Sunday.
He revised up the number of captives held from 18 to 23 but there has been no confirmation of the number from Seoul.
President Roh Moo-hyun urged the release of the South Koreans
South Korean President Roh Moo-hyun appeared on television on Saturday to say his government was making every effort to secure the safe return of his country's citizens.
South Korea has already said it plans to withdraw its troops by the end of the year.
The Koreans were taken at gunpoint in Ghazni province while travelling in a bus from Kandahar city to the capital, Kabul, on Thursday.
They were reportedly Christians on an evangelical and aid mission. At least 15 are said to be women.
The BBC's Charles Haviland in Kabul says according to a local district governor tribal elders in Ghazni are trying to negotiate with the kidnappers for their release.
The seizure was the largest-scale abduction of foreigners since the fall of the Taleban regime in 2001, according to the Associated Press.