The Ukrainian leader had said during a visit to the flashpoint southeastern city of Mariupol that "we have managed to free 1,200 of our prisoners" since a truce deal with the insurgents was struck on Friday.
A source close to the president told AFP that Poroshenko meant to say that the rebels had seized nearly 1,200 people during the conflict.
The rebels have released 648 captives since the fighting broke out in mid-April, the source said, and more than 500 are expected to be freed soon.
Mariupol, a major port and heavy industry hub on the Sea of Azov, has been in the sights of rebels apparently seeking to carve out a land corridor between Russia and the annexed Crimean peninsula.
