Mr. Sankoh, who heads the Revolutionary United Front (RUF), is reported to be preparing to return to the capital, Freetown, by road, accompanied by supporters, he added.
Meanwhile, the UN mission in Sierra Leone has sent a "strong protest" to the RUF concerning "repeated blockage of UN personnel who in theory have complete freedom of movement," the spokesman said.
In the latest incident on Saturday, a group of 17 Ghanaian peacekeepers and seven military observers were blocked by RUF fighters on the road from Kenema to Koidu, in the eastern part of Sierra Leone. The RUF fighters would initially not let the peacekeepers advance or retreat, but eventually ordered them to leave. They arrived safely back in Kenema on Sunday morning, the UN spokesman said.