Reports from the United States say a man who claimed to be a leading Taliban negotiator in secret talks with Afghan officials is, in fact, a fake.
The New York Times newspaper reports Afghan officials thought they were negotiating with Mullah Akhtar Mohammed Mansour, one of the group's top commanders - but it appears he may not even have been a member of the Taliban.
He is said to have travelled from Pakistan and reportedly had three meetings with government officials.
The fake Taliban leader was flown to Kabul on a NATO aircraft and taken to the presidential palace to meet Mr Karzai.
The BBC reports doubts about the man's identity arose after someone who knew Mr Mansour told Afghan officials he did not recognise the impersonator.
Diplomatic sources say he was paid "a lot of money", then he disappeared.
President Hamid Karzai has denied meeting the man. He says most reports about meetings with the Taliban are lies.