Greece on Thursday made a 459-million-euro ($497-million) loan payment to the IMF, an official said.
"The payment order has been given," a finance ministry source told AFP.
Greece's precarious finances have been closely monitored since the arrival of a new hard-left government in January.
The new government is engaged in difficult negotiations to renegotiate the terms of its EU-IMF bailout, and as a result has received no money left in the multi-billion loan package.
Later this month, Athens has to make interest payments of nearly 400 million euros and roll over 2.4 billion euros in six- and three-month treasury bills due to mature on April 14 and 17.
Athens on Wednesday raised 1.14 billion euros in six-month treasury bills. On Thursday it announced the sale of another 625 million euros in three-month bills next week.