Greek banks to stay closed at least until Friday - bankers

ATHENS (Reuters) - Greece's banks will stay closed at least until Friday, four banking sources said on Monday, as the country tries to reopen bailout negotiations with official creditors and save its financial system from collapse.

Greece issued a decree last week imposing capital controls and ordered banks to close after the European Central Bank (ECB) froze a vital financial lifeline following the breakdown of bailout talks between Athens and its foreign creditors.

The crisis has deepened further following Greek voters' rejection in a referendum on Sunday of the terms of the country's international aid bailout, sharply increasing the risk of Greece leaving the euro zone.

Banks are struggling to keep their automated teller machine (ATM) networks fed with banknotes and dispense cash at the set daily withdrawal limit of 60 euros, gradually using up the remaining cash buffer in the system.

"The bank holiday will be extended until Friday or next Monday," one senior banker told Reuters.

The decree expires on Monday and the government is expected to issue a new decree to replace it. Senior bankers are expected to meet the finance minister about the situation later on Monday.

Without fresh emergency liquidity assistance (ELA) from the Greek central bank, bankers estimate that the availability of cash may start tightening after two to three days, which could lead authorities to lower the daily withdrawal limit.

"With the amount of remaining cash in the system, it is not certain that we can go until the end of the weekend at the daily limit of 60 euros," said another banker, who expected the ECB to keep the ELA funding cap at 89 billion euros on Monday.

(Reporting by George Georgiopoulos, editing by Deepa Babington and Gareth Jones)