The euro zone planning to save Greece from bankruptcy is not up for renegotiation, Germany has warned, ahead of urgent talks with Greece and France.
Foreign Minister Guido Westerwelle said "[What] we just agreed last week cannot be placed back on the table". Greek PM George Papandreou is to meet France's Nicolas Sarkozy and Germany's Angela Merkel later on Thursday.
The meetings come a day after Mr Papandreou said Greece would hold a referendum on the euro zone rescue plan. Overnight, Greece's cabinet gave unanimous backing to Mr Papandreou's controverisial plan for a public vote, which could take place in December.
He told an emergency cabinet meeting a referendum would offer "a clear mandate" for austerity measures demanded by euro zone partners.
Earlier, stock markets recorded big drops amid shocked reactions in euro zone capitals to the referendum announcement.