Germany, France press Greece to make fast, credible proposals

(Adds comments by U.S. Treasury secretary and by Japanese economics minister)

* Merkel, Hollande urge Tsipras to move fast

* Tsipras calls Merkel, promises new Greek proposals on Tuesday

* Varoufakis resigns, saying euro zone peers forced him out

* ECB maintains tight grip on Greek banks

* Tsipras calls Juncker, Hollande

By Julien Ponthus and Lefteris Papadimas

PARIS/ATHENS, July 6 (Reuters) - France and Germany told Greece on Monday to come up with serious proposals in order to restart financial aid talks, a day after Greeks voted overwhelmingly to reject more austerity.

German Chancellor Angela Merkel and French President Francois Hollande, the euro zone's most powerful leaders, said Athens must move quickly if it wants to secure a cash-for-reform deal with creditors and avoid crashing out of the single currency.

Raising the pressure on Greek Prime Minister Alexis Tsipras before a euro zone summit on Tuesday, the European Central Bank decided to keep a tight grip on funding to Greek banks.

By voting decisively against tough bailout conditions, as Tsipras had urged them to do, Greeks have strengthened his negotiating hand. But the crisis remains acute, with the country's banks already closed for more than a week to avoid a massive outflow of money that could lead to their collapse.

Only emergency support from the ECB is keeping the banks afloat and saving Greece from a chaotic euro exit that would inflict more pain on its people and gravely damage the currency, the strongest symbol of the EU's drive for an "ever closer union" on a continent once ravaged by two world wars.

In a warning shot to the banks, the ECB raised the amount of collateral they must post for any loans. The move does not affect the lenders right away, but served as a reminder that their fate lies in its hands.

In a sign that Athens is keen to seek a new deal, Greece's combative finance minister, Yanis Varoufakis, resigned, apparently under pressure from other euro zone finance ministers who did not want him as a negotiating partner.

Tsipras had earlier promised Merkel that Greece would bring a proposal for a deal to Tuesday's summit, a Greek official said. It was unclear how much it would differ from other proposals rejected in the past.

Late on Monday, the prime minister's office said Tsipras had spoken with EU Commission President Jean-Claude Juncker and Hollande. His office did not provide details about the conversations.

After talks with Hollande earlier in the day in Paris, Merkel said, "We say very clearly that the door for talks remains open and the meeting of euro zone leaders tomorrow should be understood in this sense."