A man walks past the headquarters of Puerto Rican power utility PREPA in San Juan, June 30, 2015. Reuters/Alvin Baez-Hernandez

(Reuters) -- Puerto Rico's power authority PREPA has reached a tentative debt restructuring deal with bond insurers including Assured Guaranty (AGO.N) and MBIA Inc.'s (MBI.N) National Public Finance Guarantee, according to two sources familiar with the matter. The deal still needs the approval of the PREPA board, the sources said, but has been signed by representatives for all parties in the negotiations.

PREPA has been working for months to restructure more than $8 billion in debt. It previously reached deals with lenders and bondholders, but those agreements cannot be implemented without support from the insurers.

(Reporting by Nick Brown; Editing by Bernard Orr)