Updated

Sen. Robert Menendez had an unpaid intern working in his New Jersey office who was an illegal immigrant and a registered sex offender and now is under arrest by immigration authorities, The Associated Press has learned. The Homeland Security Department instructed federal agents not to arrest him until after the Nov. 6 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 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 for the Homeland Security Department, Peter Boogaard, said in an email to the AP that ICE followed standard procedures working with local prosecutors before taking what he called "appropriate enforcement action." Boogard also said AP's report was "categorically false." He did not immediately respond to a request to specify what might be false.

Menendez, a Democrat 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 television. "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. Sanchez declined to be interviewed from jail.

The prosecutor's office in Hudson County, New Jersey, said Sanchez was found to have violated the law in 2010 and subsequently required to register as a sex offender. The exact charge was unclear because Sanchez was prosecuted as a juvenile and those court records are not publicly accessible. The prosecutor's office confirmed to AP that Sanchez registered as a sex offender, although his name does not appear on the public registry. The acting county prosecutor, Gaetano Gregory, is a Republican.

Authorities in Hudson County notified ICE agents in early October that they suspected Sanchez was an illegal immigrant who was a registered sex offender and who may be eligible to be deported. ICE agents in New Jersey notified superiors at the Homeland Security Department because they considered it a potentially high profile arrest, and DHS instructed them not to arrest Sanchez until after the November election, one U.S. official told the AP. ICE officials complained that the delay was inappropriate, but DHS directed them several times not to act, the official said.

It was not immediately clear why federal immigration authorities would not have been notified sooner about Sanchez's status.

During discussions about when and where to arrest Sanchez, the U.S. reviewed Sanchez's application for permission to stay in the country as part of President Barack Obama's policy to allow up to 1.7 million young illegal immigrants avoid deportation and get permission to work for up to two years. As a sex offender, he would not have been eligible. Citizenship and Immigration Services, which oversees the program known as Deferred Action for Childhood Arrivals, notified Sanchez of that shortly before his arrest, one official said.

Menendez said the arrest spoke to the need for comprehensive immigration reform that brings illegal immigrants out of the shadows.

"It does speak volumes about why we need comprehensive immigration reform," the senator said. "I can't know who is here to pursue the American dream versus who is here to do it damage if I cannot get people to come forth out of the shadows, go through criminal background checks and then determine who is here to pursue the dream and make sure that those who are here and have criminal backgrounds ultimately get deported."