Two foreigners and two Afghans working for the International Committee of the Red Cross (ICRC) have been kidnapped in central Afghanistan, police say.
They say that the abductions took place in Wardak province.
They were reported to have taken place after the Red Cross officials travelled to meet Taleban militants to discuss the release of a German national.
Kidnappings have soared in Afghanistan where foreign and Afghan troops are battling the Taleban.
The Red Cross office in Kabul has not yet commented on the reports.
The ICRC played a key role in the release of the South Koreans
The BBC's Pam O'Toole says that the ICRC has now been working in Afghanistan for 20 years, a period spanning the end of the Soviet occupation of Afghanistan, the Afghan civil war, Taleban rule and more recently the rise of the Taleban insurgency against the elected government of President Karzai.
Our correspondent says that Afghanistan is one of the organisation's biggest operations worldwide with more than 1,000 Afghan and international staff.
Recently the ICRC hit the headlines when it helped to negotiate the release of a group of more than 20 South Koreans kidnapped by the Taleban.
But much of its work is carried out quietly behind the scenes, visiting detainees held as a result of the conflict by the Afghan authorities or international forces, helping families trace relatives with whom they have lost contact, or helping to provide medical or other aid to civilians affected by the violence.
An unnamed official told the Associated Press that the ICRC staff had gone to Wardak province to discuss the release of a German man kidnapped in July.
On Monday, two Italian soldiers who were believed kidnapped last week were freed in a military operation.
Elsewhere in Afghanistan, two Danish soldiers were killed in an attack by the Taleban in the southern province of Helmand on Wednesday.
Another two Nato soldiers were injured in the attack.