Federal agents are investigating a $300 million contract to help rebuild Puerto Rico’s power grid, The Wall Street Journal reported Monday, citing anonymous sources.

F.B.I. agents from the San Juan field office are looking into circumstances surrounding the disaster-recovery deal the Puerto Rico Electric Power Authority, the public power company known as Prepa, signed with Whitefish Energy Holdings, the paper reported, citing “three people familiar with the matter.”

Gov. Ricardo A. Rosselló announced Sunday that he had decided to cancel the contract to help restore Puerto Rico’s devastated power grid, because of the controversy that had begun to detract from the work being done.

The report came on the same day that United Nations experts faulted the United States’ response to hurricane devastation on the island, calling it ineffective and lagging far behind the support provided for other storm-struck states.

More than five weeks after Hurricane Maria struck Puerto Rico with winds of up to 155 miles an hour, conditions remained “alarming” for the island’s 3.5 million people, the group of 11 United Nations independent experts said, calling for a “a speedy and well-resourced emergency response.”

Thousands left homeless by the storm had no relief in sight, about 30 percent of normal power was being generated, few of the island’s hospitals were functioning, and there were reports that available water supplies were contaminated, the experts said in a statement.

“We can’t fail to note the dissimilar urgency and priority given to the emergency response in Puerto Rico, compared to the U.S. states affected by hurricanes in recent months,” said Leilani Farha, the United Nations special rapporteur on housing.

Soon after the deal with Whitefish was announced, questions were raised as to how a two-man company from Montana managed to secure such a lucrative contract. The company has ties to the secretary of the interior, Ryan Zinke, but both sides say there was no wrongdoing.

A House committee is investigating, and the governor has asked the island’s comptroller and the inspector general of the Department of Homeland Security to also review the deal.

The F.B.I. national office referred questions about the report to the Puerto Rico field office. A spokesman there, Carlos Osorio, said the agency could not confirm or deny the existence of an investigation.

“While Whitefish is not aware of any such investigation, Whitefish is committed to full cooperation with any inquiry or investigation,” the company said in a statement. “The procurement of the Prepa contract was at all times fully appropriate. Our focus continues to be on our work in Puerto Rico completing the work Prepa has tasked Whitefish to complete including the repair of the second major transmission line.”

A spokeswoman for the power authority said the agency had no information about an investigation, and therefore had no comment.

The governor’s office said it welcomed an inquiry.

“We have not received any information about the F.B.I. looking into the contract, but Governor Rosselló welcomes any investigation by the federal authorities and he has been clear: there should be an investigation on this matter, and if there is any wrongdoing, the persons responsible should be prosecuted to the full extent of the law,” said Yennifer Álvarez, the governor’s spokeswoman. “That’s why the Governor has asked for investigations by the Comptroller of Puerto Rico and the Inspector General of the Department of Homeland Security, John Roth.”

In a phone interview, Ms. Farha, an independent expert reporting to the United Nations, said it was “very worrying” that she had not been able to obtain clarity on the number of people who were still homeless after the storm. She noted that estimates of the number of houses destroyed ranged from 30,000 to 90,000.

Thousands of engineers had been deployed in Texas and Florida to reconnect homes to the electricity grid after hurricanes hit those states, a number far in excess of the crews deployed to Puerto Rico.

“FEMA is overall responsible,” Ms. Farha said, referring to the Federal Emergency Management Agency. “I don’t understand why FEMA can respond so quickly and affirmatively in Texas and why they weren’t deployed similarly in Puerto Rico.”

Officials have said that deploying utility crews to an island posed far greater challenges than getting them to communities on the mainland.