CARACAS, Venezuela — Many parts of Venezuela remained without power and communications on Sunday after several days of the country’s worst blackouts, which forced some hospitals to treat patients without electricity and compounded an economic and political crisis.

Power returned to some areas as engineers sought to restore service, but frustration mounted among people already struggling with hyperinflation as well as shortages of food and medicine. Witnesses reported overnight protests in a few Caracas neighborhoods and the remains of makeshift barricades and burned debris were seen at some intersections.

Some hospitals have cared for their most critically ill patients with the help of generators, but many have had to operate without power since the blackouts started Thursday afternoon, endangering vulnerable patients who rely on oxygen concentrators, dialysis machines and other equipment.

The Venezuelan government has not commented on the impact of blackouts on the sick, but Julio Castro, a doctor who supports opposition leader Juan Guaido, said a hospital in the city of Maturin reported 15 deaths linked to outages.

Castro, who joined Guaido on Sunday at a news conference addressing the energy crisis, noted that Venezuela annually designates March 10 as a day to honor the medical profession.

“We have nothing to celebrate,” Castro said.

Guaido, the leader of the National Assembly, said it was difficult to assess the impact of power cuts on the sick because of an alleged government cover-up. He declared himself interim president in late January, saying Maduro is an illegitimate leader and should resign so elections can be held. Maduro has described Guaido as a “clown and puppet” in a U.S.-backed plot to overthrow his government.

In Caracas, Alexis Reynoso, 46, said he left his home in the Venezuelan capital on Sunday morning to try to buy water and food, but most shops were closed. He said those that were open only accepted cash, but he didn’t have enough because the bank only allows small withdrawals and debit card payments aren’t possible because of the outage.

The government and opposition accuse each other of being responsible for the infrastructure breakdown. Maduro on Sunday tweeted that “multiple cyberattacks” caused the blackouts and disrupted efforts to fix the national grid. He says he hopes power can be restored in coming hours.

Guaido and his ally, the United States, say Maduro’s allegations that they sabotaged the power system are absurd. They say government corruption and mismanagement caused the decay of Venezuela’s infrastructure over many years, a situation that has contributed to the departure of more than three million Venezuelans from their country in the past few years.

“If I could, I would take the little that I have and leave the country,” said Renee Martinez, a 31-year-old Caracas resident. “This is unbearable. Here, everything is scarce and now power is as well.”

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Associated Press journalist Jorge Rueda contributed.