(CNN) Some 3.4 million Americans are facing "alarming" conditions more than a month after Hurricane Maria struck Puerto Rico, UN human experts said, calling the disaster response there ineffective compared with the urgency of federal aid to storm-ravaged states on the US mainland.

A panel of 11 experts said Monday that the hurricane aggravated an already dire situation brought on by debt and austerity. Few hospitals are functioning, some residents are left to consume contaminated water, and thousands are displaced "without any relief in sight," the experts said in a statement

As of Tuesday, only about 30% of Puerto Rico's power was back online, according to the US commonwealth's government.

"We can't fail to note the dissimilar urgency and priority given to the emergency response in Puerto Rico, compared to the US states affected by hurricanes in recent months," said Leilani Farha, the UN special rapporteur on housing.

The criticism of the US response comes amid a preliminary FBI inquiry into a $300 million contract between the Puerto Rico Electric Power Authority and Whitefish Energy Holdings, according to a source with knowledge of the inquiry.

The energy firm was contracted to rebuild the electrical grid destroyed by Hurricanes Maria and Irma last month.

Members of Congress have raised concerns over the manner in which the contract was awarded to the small Montana company. The Federal Emergency Management Agency also has questioned the amount of the contract.

The company has ties to the Trump administration. It's based in Whitefish, Montana, the small hometown of Interior Secretary Ryan Zinke, and the CEO is an acquaintance of Zinke's. An investment firm that owns a major stake in the company is run by a donor to Trump's presidential campaign.

The company, Zinke, the White House and the Puerto Rico Electric Power Authority have denied any wrongdoing.

The Puerto Rican utility is working to cancel the controversial contract.

Juan Pablo Bohoslavsky, a UN expert on foreign debt and human rights, said access to health, food, education, housing, water and social security on the island had been "massively undermined" by the economic and financial crisis that predated the disaster. Nearly half the population was living below the poverty line before Hurricane Maria struck on September 20, according to the UN experts.

"With winter approaching, we call for a speedy and well-resourced emergency response that prioritizes the most vulnerable and at risk -- children, older people, people with disabilities, women and homeless people," the UN experts said in their statement.

With about 90,000 homes destroyed and the island's most valuable exports -- banana and coffee -- hit hard, residents were "at their most vulnerable" and facing immediate food shortages, the experts said.