WASHINGTON — U.S. Sen. Robert Menendez employed as an unpaid intern in his Senate office an illegal immigrant who was a registered sex offender, now under arrest by immigration authorities, The Associated Press has learned. The Homeland Security Department instructed federal agents not to arrest him until after Election Day, a U.S. official involved in the case told the AP.

Luis Abrahan Sanchez Zavaleta, an 18-year-old immigrant from Peru, was arrested by U.S. Immigration and Customs Enforcement agents in front of his home in New Jersey on Dec. 6, two federal officials said. Sanchez, who entered the country on a now-expired visitor visa from Peru, is facing deportation and remains in custody. The officials spoke on condition of anonymity because they were not authorized to discuss details of Sanchez’s immigration case.

A spokesman said the Homeland Security Department would provide a statement later Wednesday.

Menendez (D-N.J.), who advocates aggressively for pro-immigration policies, was re-elected in November with 58 percent of the vote. He said his staff was notified Monday, and he personally learned about the case from AP’s reporting and knew nothing about whether DHS delayed the arrest. The senator said his staff asks interns whether they are in the country legally but cannot check to be sure.

“We certainly wouldn’t have known through any background checks since he is a minor about any sex offender status,” Menendez said in an interview Wednesday with MSNBC. “Once it came to our attention, our New Jersey staff director let the young man go.”

Online jail records did not indicate whether Sanchez has an attorney. Immigration officials there were relaying a request from the AP to speak with Sanchez in jail.