Mexico's federal authorities opened an investigation Wednesday into whether a governor illegally built a river dam on his family's ranch property that may have affected local water supplies.

The accusations came amid a clash between federal officials and Sonora Governor Guillermo Padres, who said the allegations were a bid to discredit him over his complaints that authorities mishandled a devastating copper mine spill.

David Korenfeld, director of the National Water Commission, said inspectors would check whether the ranch's owners had permits to build the dam and whether it has affected the city of Hermosillo and others in the northwestern state.

"(The commission) acts according to the law, whoever the owner may be," Korenfeld told a news conference, showing satellite images of the dam being built in 2011.

"If there are no permits, the dam's demolition will be ordered," he said.

Padres, a member of the opposition conservative National Action Party, had voiced his own beef against the federal authorities.

Padres took out a full-page newspaper advertisement addressed to President Enrique Pena Nieto, accusing federal officials of ignoring residents' warning of an imminent risk of a spill at the Grupo Mexico-owned mine.

He called for the dismissal of the local representatives of the federal environmental protection agency and the water commission

On August 6, some 40,000 cubic meters (10.6 million gallons) of sulfuric acid leaked out of a holding tank at the Buenavista mine and into the Sonora River, forcing authorities to cut off water supplies to 20,000 people.

In his newspaper ad, Padres also rejected the accusations over the dam.

"No current or future campaign to discredit me or my family will distract me from pointing out those guilty of Mexico's worst environmental disaster," Padres wrote.

The president's spokesman, Eduardo Sanchez, hit back, saying federal authorities had acted promptly and efficiently to deal with the spill.

"We demand that the Sonora state government act within the law," Sanchez said, adding that the decision to keep or fire federal representatives "is exclusive authority of the president and not the governor of that state."