NICOSIA, Cyprus (AP) — U.N. Secretary-General Antonio Guterres is attending Cyprus peace talks in Switzerland in an effort to bridge differences between the rival sides.

Guterres' appearance Thursday is his second during the nine days of negotiations, which have so far failed to achieve much progress in reunifying the ethnically divided Mediterranean island nation as a federation.

Key to progress in the talks between Greek Cypriot President Nicos Anastasiades and the leader of the breakaway Turkish Cypriots Mustafa Akinci will be the input of Cyprus' so-called guarantors — Greece, Turkey and Britain.

The European Union is also attending. EU foreign policy chief Federica Mogherini said the EU fully backs the talks and that she's optimistic. Cyprus is an EU member EU but only the internationally recognized Greek Cypriot south enjoys the benefits of membership.