MEXICO CITY — The bodies of three photojournalists were found dismembered on Thursday in the eastern state of Veracruz, days after a crime reporter for a national magazine was killed in her house there.

The motives for the killings were not immediately known, and few such cases in Mexico are ever solved. But human rights groups condemned the deaths as another worrying sign of the vulnerability of journalists reporting on the wave of drug and organized crime violence that has rocked Mexico in the past six years and left more than 50,000 people dead.

“What we have seen in Mexico in the last years is a systematic attempt to muzzle the press that has been successful in various parts of the country, where the press has been effectively censored,” said Rosental Alves, director of the Knight Center for Journalism in the Americas, in Austin, Tex. “This unprecedented blood bath is fueled by a certainty of impunity, as the cases of crimes against the press usually don’t even reach a court of law.”

The Veracruz journalists killed this past week were the first documented killings of Mexican journalists this year, according to press groups; last year, 11 were killed and, according to Article 19, a press freedom group, 44 have been killed in the past six years as drug crime soared and the government began an offensive.