April 28 (Reuters) - Spain's grid operator has restored electricity supplies to about half of the country after a huge power outage brought the Iberian Peninsula to a standstill on Monday, and the rest should be restored by Tuesday, Prime Minister Pedro Sanchez said.
Authorities were yet to establish what had caused the blackout and were not ruling out any hypothesis, he added in a televised address.
(Reporting by Joan Faus and Inti Landauro; Writing by Andrei Khalip; Editing by David Latona)
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