Ex-Liberian President Charles Taylor, jailed for war crimes, is reported to have phoned political allies from inside a UK maximum security prison.
A recording of the alleged call, in which he reportedly advises his party members on tactics, was obtained by Africa Confidential magazine.
He is serving a 50-year sentence for supporting rebels who committed atrocities in Sierra Leone.
The Ministry of Justice said it does not comment on individual cases.
Alain Werner, director of Civitas Maxima, an NGO which builds legal cases against alleged Liberian war criminals, said the allegation was “extremely worrying”.
The call, which has been heard by the BBC, is thought to have been made from a landline inside HMP Frankland, near Durham, on 28 January, Taylor’s 69th birthday.