Yanis Varoufakis, a firebrand who had infuriated European counterparts, announced he was resigning at Prime Minister Alexis Tsipras's request in a move to placate creditors.
He was replaced by Euclid Tsakalotos, a much more discreet and calm junior foreign minister and economist who had been Greece's pointman in the negotiations with creditors.
Varoufakis's departure came a day after Greek voters overwhelmingly rejected more austerity required by international creditors under a bailout deal, heightening fears of a "Grexit".
"It is not about people but rather positions," Chancellor Angela Merkel's spokesman Steffen Seibert said, adding there was currently "no basis to enter into negotiations on a new aid programme".
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"It is up to Greece" if it wants to stay in the eurozone, he said. "We are waiting to see which proposals the Greek government makes to its European partners."
A Greek government source said Tsipras and Merkel had spoken by phone and agreed Athens' proposals would be presented at a hastily-called eurozone summit tomorrow.
Berlin's reluctance to reopen talks underlined a divide within Europe over the Greek crisis, with France, Italy and Spain adopting a more conciliatory tone.
Italian Prime Minister Matteo Renzi said on his Facebook page that Europe needed to "talk not only about austerity and balance sheets but about growth, infrastructure", while Spain said it was open to new negotiations for a new Greek bailout.
And although last week Greece defaulted on a 1.5 billion euro repayment to the IMF, effectively cutting it off from further financial assistance from the fund, IMF chief Christine Lagarde said it was "monitoring the situation" and stood "ready to assist Greece if requested to do so".
After jubilant celebrations by 'No' voters following their 61-percent referendum victory, Greeks returned to the reality of closed banks and queuing at ATMs for their daily withdrawal limit of 60 euros.
Fears were growing that the cash machines could soon run out despite government-enforced caps on withdrawals, and emergency funding was urgently needed from the European Central Bank (ECB) to stave off economic collapse.