"A 'No' vote is a decisive step toward a better agreement that we aim to sign right after Sunday's result," he said, rejecting repeated warnings from European partners that the referendum would effectively be a vote on whether Greece stays in the euro or returns to the drachma.
European Council President Donald Tusk retorted in a tweet: "Europe wants to help Greece. But cannot help anyone against their own will. Let's wait for the results of the Greek referendum."
Euro zone finance ministers held an hour-long conference call to discuss the previous night's offer from Tsipras, but were adamant that no further discussions would be held until after Sunday's vote.
"We will come back to your request for financial stability support from the ESM (European Stability Mechanism) only after, and on the basis of the outcome of, the referendum," the head of the currency zone ministers' Eurogroup, Jeroen Dijsselbloem, wrote in a letter to Tsipras.
IMF Managing Director Christine Lagarde told Reuters in an interview that she would want to see reforms before opening discussions on any new debt package.
Global financial markets have reacted remarkably calmly to the widely anticipated Greek default, strengthening the hand of hardline euro zone partners who say Athens cannot use the threat of contagion to weaker European sovereigns as a bargaining chip.
In his overnight letter to creditors, seen by Reuters, Tsipras agreed to accept most of their demands for taxes and pension cuts and asked for a new 29 billion euro loan to cover all debt service payments in the next two years.
However, even if negotiations do restart after the referendum, Germany and others made clear that any talks on a new program would have to start from scratch with different conditions.
Read MoreGreek letter: Are the concessions enough?
The exasperated tone to public comments of European leaders exhausted by the chaotic turnarounds of the past few days offered little hope of a breakthrough.
Tsipras has suggested he would step aside if Greeks vote "Yes" in Sunday's referendum.
"This government has done nothing since it came into office," German Finance Minister Wolfgang Schaeuble said in a speech in the lower house of parliament in which he accused Athens of repeatedly reneging on its commitments.
"You can't in all honesty expect us to talk with them in a situation like this," he said.
French Finance Minister Michel Sapin, among Greece's strongest sympathizers in the euro zone, told RTL radio, "The aim is to find an agreement before the referendum if possible ... But it's dreadfully complicated."
Lagarde declined to be drawn out on whether she viewed Tsipras was a reliable negotiating partner after his latest switch, although she did say the Fund wanted to see evidence of reforms before talks about any new potential debt package.
"We have received so many 'latest' offers, which themselves have been validated, invalidated, changed, amended, over the course of the last few days, that it's quite uncertain exactly where the latest proposal stands," she said.