JOHNSTON COUNTY, N.C. — U.S. Immigration and Customs Enforcement agents arrested Wednesday 21 illegal immigrants working for construction companies at Camp Lejeune, the agency said.

The workers were from Guatemala, Honduras, El Salvador and Mexico and most had counterfeit immigration documents.

Fifteen of the 21 workers were transported to the Johnston County Jail Wednesday evening because the sheriff there signed a contract with the federal government to house suspected illegal immigrants who had been arrested

"I believe, as a sheriff, I have an obligation to help the federal government get illegal aliens off the streets of our county, our state and our nation," Johnston County Sheriff Steve Bizzell said.

This marks the fourth time in as many months that workers at military installations in North Carolina have been arrested.

Last month, three men believed to be illegal immigrants landed jobs at Fort Bragg's Special Warfare School teaching foreign languages to elite forces. In August, a tip led federal agents to arrest 39 suspected illegal immigrants at Camp Lejeune. And in July, nearly 50 men who worked on construction projects were arrested at Seymour Johnson Air Force Base.

On Wednesday, two people from Senegal and one from Mexico were also arrested at Hartsfield International Airport, in Atlanta, where they had identity badges for access to secure areas. The arrests followed checks of records of employees at Le Petit Bistro in the airport, immigration authorities said.

Investigations were continuing, ICE spokeswoman Jamie Zuieback said.

"Unauthorized workers employed at sensitive sites, such as airports and defense facilities, pose serious homeland security threats," Zuieback said. "Not only are their identities in question, but they may be vulnerable to exploitation by terrorists and other criminals given their illegal status in the United States."