Native American burial sites have been blown up by construction crews building the US-Mexico border wall, says a lawmaker and tribal leaders.
Authorities confirmed that “controlled blasting” has begun at Arizona’s Organ Pipe Cactus National Monument, a Unesco recognised natural reserve.
Raul Grijalva, a Democratic congressman, called the destruction “sacrilegious”.
The government failed to consult the Tohono O’odham Nation, he said.
Environmental groups also warn of the damage being done to the local underground aquifer, as well as to migrating wildlife in the remote desert region about 115 miles (185km) west of Tucson.
Officials say the aim of the project is to construct a 30ft-tall (9m) steel barrier that runs for 43 miles on the national park land.