"Tomorrow (Wednesday) the representatives of the four institutions will be in Athens," the source said, referring to the European Union, the European Central Bank, the European Stability Mechanism and the International Monetary Fund.
Technical teams from the four institutions yesterday had already begun hammering out the final terms for a rescue package worth up to 86 billion euros (USD 94 billion).
The talks started after the Greek parliament passed two sets of reforms demanded by the eurozone as part of a bailout deal sealed at a tense summit last month.
Athens and Brussels hope the terms of the new bailout can be finalised by mid-August, with cash-strapped Athens facing a 3.2 billion euro repayment to the ECB on August 20, and a 1.5 billion euro reimbursement to the IMF the following month.
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However, there was confusion in Athens after Brussels indicated yesterday that more measures would need to be approved before funds are released.
"More reforms are expected... On the part of the Greek authorities to allow for a swift disbursement under the ESM and this is what is being discussed right now," EU spokeswoman Mina Andreeva said yesterday.
Formerly known as the 'troika', the creditors were widely loathed in Athens as enforcers of ruinous austerity policies before the government of leftist Prime Minister Alexis Tsipras kicked them out earlier this year.
The mission chiefs of the EU, ECB and IMF had last been in Greece in September.