Border Patrol agent Nicolas Ivie was shot dead and another agent wounded when they came under fire on Tuesday while responding to a tripped ground sensor in a drug smuggling corridor in Arizona near the border with Mexico, authorities said.
Authorities said three agents were on foot about 5 miles north of the border in rocky terrain when gunfire erupted well before daybreak, but provided few additional details on the circumstances of the violence.
"As they were walking up the trail, they reported taking gunfire," Cochise County Sheriff's spokeswoman Carol Capas said. "We have unknown suspect or suspects at this point."
The shooting marked the fourth conflict-related death of a Border Patrol agent in Arizona in less than two years and reignited concerns about border security in a state that is already at the forefront of the national immigration debate.
"Flags will be lowered in honor of the slain agent. Elected officials will vow to find those responsible. Arizonans and Americans will grieve, and they should. But this ought not only be a day of tears," Republican Governor Jan Brewer said in a statement.
"There should be anger, too. Righteous anger - at the kind of evil that causes sorrow this deep, and at the federal failure and political stalemate that has left our border unsecured and our Border Patrol in harm's way," added Brewer, a vocal foe of President Barack Obama's administration on immigration.
Brewer, citing what she described as a federal failure to secure Arizona's southern border, signed a broad immigration crackdown into law in 2010 to try to crack down on the flow of illegal immigrants into the state where an estimated 360,000 undocumented people live.
Critics of the law, which includes a requirement that police check the immigration status of anyone they stop and suspect of being in the country illegally, have said it could lead to racial profiling. Read more