Mexican authorities were searching Thursday for two missing human rights defenders whose bullet-riddled vehicle was found abandoned, officials said, following an urgent appeal by the United Nations to find them.

Ricardo Lagunes, a lawyer, and Antonio Diaz, a professor, went missing in Michoacan state on Sunday after attending a community meeting.

Michoacan, on central Mexico's west coast, is home to a contentious iron ore mine.

The men told their relatives that they were returning home but were not heard from again, the Michoacan prosecutor's office said in a statement.

On Sunday night, police in the neighboring state of Colima found their truck damaged by gunfire, it said, adding that security forces and police dogs were searching for them.

The Mexican office of the United Nations High Commissioner for Human Rights issued "an urgent call" for authorities to find the activists safe, adding that at least one of the men was supposed to be under state protection.

"It's unacceptable that those who defend our rights have to do so at the cost of their freedom, their integrity or their lives," the UN agency said.

Mexico is considered one of the world's most dangerous countries for human rights defenders, particularly those involved in disputes over land and mining.

In 2021, 54 environmental activists were killed in the Latin American nation, the most in the world, and impunity "remains rife," according to the London-based watchdog Global Witness.