Greek Prime Minister Alexis Tsipras on Friday said the IMF should stop tinkering with the country's latest bailout with European creditors, blaming the global lender for causing a delay in talks.

The IMF has worked with the EU on two previous Greek bailouts but said it would not participate in the latest plan without credible reforms and an EU agreement to ease Greece's debt burden.

"Greece fails to understand why the IMF insists in changing the design of the reforms in a way that leaves their yield and simplicity intact, but makes the reform significantly less progressive," Tsipras said in an article published in the Financial Times.

"Delaying the conclusion of the first review of the ESM (European Stability Mechanism) programme by stubbornly insisting to ignore the letter and the spirit of the agreement does not serve the principles on which Europe has been thriving," Tsipras said.

Leftist Tsipras has repeatedly lashed out at the Washington-based global lender, and the current talks have been clouded by allegations that senior IMF officials sought to engineer a Greek default.

A WikiLeaks report earlier this month said the IMF was looking for a crisis "event" to push Greece and European negotiators into accepting its fiscal targets, citing an intercepted conversation between senior IMF officials.

IMF chief Christine Lagarde later dismissed this notion as "nonsense".

Lagarde on Thursday said the IMF had no intention of withdrawing from the programme, but hinted its role could change, without going into details.

"We will not walk away. Our form of participation may vary, depending on the commitments of Greece and the undertaking of the European partners. But we will not walk away," Lagarde said.

The IMF chief said she agreed with Athens that the talks needed to move faster, but once again called into question forecasts on Greece's economy not vetted by her own staff.

To reach the bailout program objectives of economic stability and sustainability, she said, "there has to be real and realistic numbers and sustainable measures."