In Beijing, where he has gone after taking part in crisis talks with the other ministers on Thursday, Fabius told reporters that participants had agreed not to say anything "until the end of the morning".
"The opposition, in particular, wants to be able to consult with some of its members, which is completely understandable," he told Europe 1 radio.
But the office of President Viktor Yanukovych issued a statement said that an agreement was to be signed at midday.
German Foreign Minister Frank-Walter Steinmeier and Poland's Radosław Sikorski refused to confirm the claim, saying only that there was a break after negotiations that lasted all night and that the meeting, which also involves Russia, was to start again at noon.
A source on the German delegation told the AFP news agency that no final agreement had been reached and that the negotiations had been "very difficult".