MEXICO CITY: Three nurses, all sisters, were found dead with signs of strangulation in the northern Mexican state of Coahuila, officials said on Friday, an apparent triple murder that follows a series of assaults on health workers in the coronavirus pandemic.

Officials said they were investigating a crime but that the motive was not clear. Health workers have faced increased aggression in Mexico in recent weeks over fears of contagion.

Javier Guerrero, a top official for Mexico’s main public health service IMSS in Coahuila, described the deaths of the three nurses as murders. They “happened at a moment when our health workers are the most important element to face the health crisis.”

Coahuila State Attorney General Gerardo Marquez said two or three criminals might have been involved but no arrests have been made. It was not immediately clear when the sisters died.

“Until now there is no evidence that suggests this was because of their jobs in the health sector,” he said. “It’s very regrettable for society - and I reiterate the state’s commitment to find those who are guilty and bring them to justice.”

Mexico’s health ministry calculates transmission of the virus to peak this week in Latin America’s second largest economy.

On Thursday, Mexico reported 1,982 new confirmed cases of coronavirus infections and 257 additional fatalities, the most lethal day since the pandemic reached Mexico.

The new figures bring the total number of confirmed cases to 29,616 and 2,961 deaths. However, the government has said the real number of infections is significantly higher and that deaths are also undercounted.