Mr Vlahn said the group numbered more than 3,000 fighters who were predominantly members of the Gio and Mano ethnic groups - the groups from which President Taylor drew the bulk of his support when he launched his own armed rebellion in 1989.
Defence ministry sources said the rebels had crossed from Ivory Coast on Monday night.
The man who telephoned the BBC claiming to be a spokesman for the rebels, Johannes Zogbay Vlahn, said the rebels had not received support from any government.
Earlier this year there were a number of fierce battles after rebel incursions into northern Lofa County - Liberia accused Guinea of supporting those dissidents.
No outside support
Mr Vlahn told the BBC's Focus on Africa programme that the rebels had been grouping in jungle in Nimba County while the attacks were taking place in Lofa County, and they had not crossed any border.
He said the fighters had purchased their arms on the black market.
Mr Vlahn said the group numbered more than 3,000 fighters who were predominantly members of the Gio and Mano ethnic groups - the groups from which President Taylor drew the bulk of his support when he launched his own armed rebellion in 1989.
He said the group's objective was to remove President Charles Taylor from power because he had terrorised and killed Liberians for more than 10 years and was a menace to the sub-region.
Regional power shift
Analysts say the rebels are likely to be supporters of a former ally of Mr Taylor's during the first year of his rebellion, Jackson Doe, who was killed in mysterious circumstances in 1990.
Although Mr Vlahn denied support from Ivory Coast, the change of government there is likely to alter the balance of forces in the sub-region.
The recently removed Ivorian military leader, General Robert Guei, was close to Mr Taylor's administration and his feared presidential guard included Liberian fighters.
Mr Taylor visited Ivory Coast's new President, Laurent Gbagbo, shortly after he took office but no details were given of the substance of their talks.
Mr Taylor denied General Guei had sought asylum in Liberia.