A volunteer militia that conducts its own unofficial patrols of the US-Mexico border started building a fence on Saturday aimed at stopping illegal immigrants from entering the US.
The civilian border patrol, called the "Minutemen," which advocates a tough approach to illegal immigration, held the ground-breaking ceremony in the southwestern state of Arizona on private land adjacent to Mexico.
The fence represents a first step in the militia's plans to construct fences and barriers along the 3,000km common border which it says the US government has failed to secure.
"Many have talked of building a secure fence between Mexico and the United States," the Minuteman Civil Defense Corps (MCDC) said on its Web site, www.minutemanhq.com.
"Now ... MCDC is taking action again and doing the job the federal government will not do," the organization said.
"We laid ground for the foundations and we're about to raise the fence," a spokeswoman for the MCDC, Connie Hair, said.
Several hundred people, including Minutemen and local politicians, attended the ceremony, she said.
The fence, some 2m high and 16km long, is an initial step toward a more sophisticated security system for which the Minutemen are attempting to raise funds nationwide.
The grassroots group adopted the name of the Minutemen, an elite militia that played a role in the 1775-1783 US war of independence from Britain.
It has been patrolling the US-Mexico border since April last year. The volunteers help the US Border Patrol to spot illegal immigrants, but are not authorized to arrest them.
Saturday's fence action occurred at the start of the long Memorial Day holiday weekend, when the US remembers its war dead.
And it came as the US Congress debates immigration reform, an emotional issue that has divided the nation.
The Senate approved a bill this week that would create 200,000 temporary work visas for foreigners who take low-skill jobs in the US, and double the number of US Border Patrol agents on the border with Mexico.
Most controversial is a provision that would allow many of the estimated 11.5 million foreign workers who entered the US illegally, many of them Mexican, to gain legal status.
The bill also includes funding for the construction of a 600km wall along the southern US border with Mexico.
Last December, the House of Representatives approved a tougher plan that would make unapproved US entry a federal crime.
Reconciliation of the Senate and House proposed reforms was expected to be difficult, just months ahead of the November mid-term legislative elections.