Kenya’s government said on Monday that it was gradually restoring power after the country’s third major blackout in four months, adding to rising discontent with President William Ruto over a worsening economic situation and his policies since taking office 15 months ago.

The blackout hit many parts of the country after 7:30 p.m. local time on Sunday, with Kenya Power, the state-run utility, pointing to a “suspected fault affecting the power system.”

Neighborhoods in the capital, Nairobi, were plunged into darkness, and two terminals at Jomo Kenyatta International Airport also lost power, according to the Kenya Airports Authority.

Kenya generates most of its electricity from renewable resources, including geothermal, wind and solar. But old infrastructure, corruption and illegal connections have made the grid unreliable, and ever-rising electricity taxes mean that power bills are too expensive for many Kenyans.

Jomo Kenyatta airport is among the busiest hubs in Africa, with millions of passengers every year.

The airport authority said in a statement on Sunday evening that two of the airport’s four generators — which had been tested in the past week — had “failed to immediately activate” but that the control tower and runway remained operational during the blackout.

Video footage shared on social media and broadcast on local television showed passengers finding their way through darkened terminals using the flashlights on their phones.

Kenya’s transport minister, Kipchumba Murkomen, said the government would mount an investigation into the cause of the outage.

“Considering the frequency of the power disruption, and taking into account the fact that J.K.I.A. is a facility of strategic national importance, we are making a formal request to the National Police Service to investigate possible acts of sabotage and coverup,” Mr. Murkomen said about the airport outages on Sunday evening in a statement on the social media platform X.

But on Monday, Davis Chirchir, the energy and petroleum minister, offered a less sinister explanation for the blackout, attributing it to an overload on a transmission line in western Kenya.

Mr. Chirchir said the energy grid had been long plagued by underinvestment, and he promised that the government would build a new transmission line in partnership with foreign investors and governments in the next 20 months. To ease strain on the grid, the authorities will consider rotating power cuts, he said.

“We will be scheduling some minimal load-shedding,” Mr. Chirchir said, “so that we don’t unnecessarily have to bring down the whole country because of an overload.”

Some parts of Nairobi and the coastal city of Mombasa were still without power as of Monday afternoon — a day before Kenya marks its 60th independence day.

Kenya often experiences power interruptions, but the frequency and scope of the recent outages have prompted widespread concern.

In November, it took engineers almost 10 hours to restore power after an outage affected many parts of the country. That followed a 14-hour blackout in August that paralyzed businesses and affected operations at the Jomo Kenyatta airport.

Mr. Murkomen, the transport minister, responded by firing the managing director of the airport authority and pledged that the situation would not be repeated.

At the time, Kenya Power blamed disruptions at the country’s biggest wind farm for the blackout, while the power producer pointed the finger at the national grid.

Mr. Ruto has faced searing criticism and mounting public anger as Kenya’s economic pains have grown. After coming to office in September 2022, he scrapped fuel subsidies and raised taxes, even as he hosted lavish state dinners at home and took dozens of trips abroad.

Over the past year, inflation has continued to rise, the Kenyan currency has continued to depreciate, and the costs of food and fuel have skyrocketed. Torrential rains and severe floods, exacerbated by climate change, have also wreaked havoc in recent weeks, killing dozens of people and displacing tens of thousands of others.

Until the new transmission lines are built, power outages will continue, Mr. Chirchir warned on Monday.

“It is a challenge that as a country we are really ashamed of and we need to address it,” said Mr. Chirchir, who was at the airport and had just returned to Kenya from the United Arab Emirates when the power went out.