The two sides hope to conclude the deal by the first week of next month, clearing the way for Secretary of State John Kerry to visit Havana soon afterwards for a flag-raising ceremony to upgrade the U.S. Interests Section to a full-scale embassy, the sources said.

Since a breakthrough between the two former Cold War rivals announced in December, negotiators have settled all but a few differences and were confident they would soon be resolved, several sources told Reuters.

They said the exact timetable for the formal embassy opening was unclear because of Kerry's recovery from a broken leg suffered in a May 31 biking accident in France, as well as the looming June 30 deadline for a final nuclear deal with Iran, which would dominate Kerry's schedule over the next weeks.

Restoration of relations would be the latest phase in a normalization process, which is expected to move slowly because of lingering problems over issues such as Cuba's human rights record. A U.S. embargo will remain in place, and only Congress can lift it.