(CNN) Nearly 500 more people died in Puerto Rico in September -- when Hurricane Maria struck the island -- than in the same month the previous year, according to government officials.

The acknowledgment, made during a Wednesday news conference, comes as the island's government continues to face questions about an official death toll of 55 from the massive storm that made landfall on September 20.

An official with Puerto Rico's forensics institute told reporters that 472 more people died this September than in the same month in 2016 -- up from 2,366 to 2,838.

"We are not going to say there could be more or less," Héctor Pesquera, secretary of Puerto Rico's Department of Public Safety, which oversees the count, said of hurricane-related fatalities. "We've quantified the number of deaths."

Pesquera has staunchly defended government efforts to generate an accurate count under extremely trying conditions: most lines of communication were cut and many roads on the island were initially impassable.

San Juan Mayor Carmen Yulín Cruz, a frequent critic of the disaster response, said last week that she believed the death toll could be in the hundreds and possibly as high as 500.

Many hurricane victims were not included in the official count because the cause of death was improperly recorded or they were "cataloged as dying of natural deaths," Yulín Cruz said.

"When they were, for example, hooked to a respirator, there's no power, the small generator that they had that gives up, and of course, they die of natural causes, but they are related to a lack of electricity," she said.

Pesquera called the mayor's comments irresponsible and asked her to back the claims with evidence.

Some disaster experts have also questioned the official tally.

John Mutter, a Columbia University disaster specialist who studied the death toll after Hurricane Katrina, has said he would have expected fatalities in Puerto Rico to be in the hundreds -- in part because of the level of poverty on the island, and also because so few people would have been able to evacuate, as they did for Hurricane Irma in Florida.

Mutter told CNN last month that the fact that all potential hurricane fatalities must be reviewed by a single office in San Juan was part of the problem. Some -- but not all -- of the 50 US states have coroners stationed locally by county or subregion, he said.

About 60% of the US territory, which is home to approximately 3.4 million US citizens, is still without power.