Peace adviser Echeverri is a former defence minister

Earlier, President Andres Pastrana criticised Mr Gaviria for ignoring warnings and failing to take extra security precautions.

The latest abductions come as the Colombian Government again rejected an offer by the FARC to exchange imprisoned rebels for politicians and soldiers kidnapped by the guerrillas.

Growing violence

The peace demonstrators had left the city of Medellin on Wednesday to promote non-violence and reconciliation.

They were held up just three kilometres from their destination, the north-eastern town of Caicedo in Antioquia.

FARC rebels demanded to see the governor and a delegation which included members of the Catholic Church.

Part of the delegation returned safely, but Mr Gaviria and Mr Echeverri have not been seen since.

The governor of Antioquia had said the peace march was directed against the FARC, but was a protest against all forms of violence.

Violence has been rising since the government ended a three-year peace process with FARC in February.

Among the hundreds of hostages being held by rebels is the presidential candidate Ingrid Betancourt, kidnapped in February.