Athens needs the funds to repay 7.5 billion euros ($8.2 billion) of debt maturing in July. Tsipras and German Chancellor Angela Merkel agreed during a call on Wednesday morning that a deal was "feasible" by Monday, a government official said.

"I'm optimistic," Tsipras told journalists. "The messages I'm getting are that we will have a positive outcome on the 22nd."

Tsipras has urged Greece's international lenders also to reach an agreement on easing its debt burden by May 22.

Should the lenders set out measures for implementing their commitment to longer-term debt relief, and the ECB include Greece in its bond-buying program, sources told Reuters on Tuesday that Athens was eyeing a sovereign bond issue as early as July.

"If the signal (on debt relief) is strong, we will have early tests even within the summer," Tsipras said.

Greece's last venture onto international bond markets was with two issues in 2014.