Discussions in Ukraine's capital Kiev were to end in the next few days, but will continue through next week at least, the source told AFP.
"These kind of discussions require time. There's nothing unusual about it," the person said.
The previous USD 17 billion aid program agreed in April 2014 has proven inadequate to stabilize Ukraine's finances as the country fights a pro-Russia insurgency in the industrialized east, a fight that has left more than 5,000 dead and ravaged the country's economy.
It could involve both more money and a longer period than the two-year term of last year's program.
No amount for a new program has been proposed, but the IMF has said the country needs some $15 billion more from all sources to keep its finances stable through the end of 2015.
A new deal between Ukraine and the IMF could also allow the country to begin talks with its private-sector creditors on lightening its debt service burden.
