Nigerian kidnappers have demanded a ransom of 60 million naira (£151,000) for a German archaeologist and his associate who were abducted this week from a remote northern village.
A worker at a Nigerian excavation site said he heard the demand in a telephone call to the site supervisor.
The caller warned not to involve police or security forces.
Authorities already are searching around Jenjela village in Kaduna state, where gunmen abducted Professor Peter Breunig and associate Johannes Behringer on Wednesday.
Police have not commented on the case.
The 65-year-old Prof Breunig and Mr Behringer, who is in his 20s, are part of a four-person team from Frankfurt’s Goethe University.