Investigators unearthed the skulls of 47 more suspected victims of Mexico's drug war in Veracruz state, just days after uncovering 250 skulls at a separate mass grave used by drug cartels, the state's attorney general said on Sunday.

Veracruz, on Mexico's Gulf coast, has long been a stomping ground for criminal gangs, who fight over lucrative drug and migrant smuggling routes.

Giving details on the latest grisly find, Jorge Winckler said the skulls and remains of multiple body parts were unearthed from eight unmarked graves, clustered in a 120 sq metre area, about 10 kilometers (6 miles) from the town of Alvarado.

So far, Winckler said, investigators had positively identified one three-person family, missing since September 2016, and the remains of two other men.

"The work continues," Winckler told a news conference, vowing to track down the perpetrators.

Just days earlier, investigators recovered more than 250 skulls from another unmarked grave 60 kilometers (37 miles)further north in the Gulf state of Veracruz.

That burial site was uncovered by relatives of missing family members, impatient with officials' apathetic response, who launched their own search for missing family members.

The relatives' groups have exposed the government's slow progress in attending to rights abuses and victims.

The former governor of Veracruz, Javier Duarte, who belonged to the country's ruling party, is a fugitive, fleeing organized crime charges.

Separately, on Sunday the Veracruz attorney general's office said it was investigating the murder of a journalist, Ricardo Monlui, who was shot dead in the town of Yanga.

Veracruz is the most dangerous state in Mexico for journalists. The Committee to Protect Journalists said in 2016 that at least six reporters had been killed for their work since 2010, when Duarte took office, adding it was investigating nine other cases.