"The information I have is that four of our colleagues, two expatriates and two Afghan nationals, were coming back from Wardak to Kabul yesterday but they couldn't make it," said the spokeswoman, who declined to be named.

"We have lost contact with our staff since yesterday," she said.

In August, the Red Cross helped broker talks between the Taliban and officials from Seoul that led to the release of 19 South Korean hostages after more than a month of captivity.