A bomb has exploded in the centre of the Greek capital, Athens.

Police say no-one was injured in the blast, which was caused by a home-made device, planted outside an Amercian University.

An anarchist group calling itself Anti-Power Struggle claimed responsibility in an anonymous telephone call to a private radio station in which it threatened government ministers for education and foreign affairs, Gerasimos Arsenis and Theodoros Pangalos and the head of the Greek Orthodox Church Archbishop Christodoulos.

Correspondents say that obscure groups have claimed responsibility for more than two hundred attacks in Athens last year, including bombings of the private offices of at least four government ministers.