The captives swap between Russia and Ukraine may begin before the end of this week, two diplomatic sources told Interfax on Wednesday.

"The exchange may begin before the end of this week; the probable date is September 7," one of the sources said.

The other source confirmed that the swap had been scheduled to take place on Saturday but noted that the agreement was tentative.

"Only framework agreements have been reached as of yet. The sides will agree on the precise date and terms of the swap in the middle of the week," the source said.