Last Update: 11:31
"We still think there is a need for more realism in assumptions and more specificity," Thomsen said on Tuesday.
A group of euro zone countries led by Germany wants the IMF to join the Greek bailout, now handled by euro zone governments alone, to increase credibility. The IMF says that it will only join if Greece is granted debt relief.
The basis of the discussions is a promise made by euro zone lenders in May 2016 which spells out some assumptions for the possible debt relief. The IMF wants euro zone governments to spell out the various measures in more detail.
"We accept the main assumption of the May 2016 agreement that it does not have to be finally approved, calibrated or delivered before the end of the program (bailout) but we need more specificity on what will come at the end of the program," Thomsen said.