NEW DELHI — India's government has ordered a probe into the deaths of five men asphyxiated by toxic fumes while cleaning a septic tank at a housing complex in New Delhi, an official said Monday.

Minister of Labor Gopal Rai has asked for the results of the inquiry to be ready within three days, Rai's spokesman, Sanjay Kamboj, told The Associated Press.

The men were sent into the tank to clean it on Sunday, according to New Delhi deputy police commissioner Monika Bhardwaj.

Four men were declared dead on arrival at a nearby hospital, and the fifth man died at the hospital Monday, Bhardwaj said.

Police are pursuing criminal charges stemming from the deaths, she said.

According to Bezwada Wilson of the Sanitation Workers Movement group, more than 1,800 people across India have died while cleaning septic tanks or sewers since 2014, when India's Supreme Court issued a ruling to bolster a 2013 act that prohibits employing people to clean human solid waste by hand.

"Those in power are not taking these events seriously," Wilson said.

The 2013 law calls such work "dehumanizing" and based on a "highly iniquitous caste system."

Caste prejudice is endemic in Hindu-majority India, even though the constitution outlaws the practice and has made it a crime punishable by up to a year in prison. Members of lower castes are often forced to perform jobs considered unacceptable by other castes.

The government of Prime Minister Narendra Modi has launched a massive campaign to improve public health by installing more than 80 million latrines.

But the plight of sewer and latrine cleaners remains largely unchanged, activists say.