A botched suicide mission on the New York City subway system showed in the “starkest terms” that the failures of the U.S. immigration system are a national security issue, U.S. Attorney General Jeff Sessions said Tuesday during a stop in Baltimore with the new Homeland Security chief.

Speaking at a news conference at the U.S. Attorney’s office in Baltimore, Sessions said two terrorist incidents in New York in the last two months were each carried out by men who were in the U.S. “as a result of failed immigration policies.”

A 27-year-old Bangladeshi immigrant is in custody after Monday’s rush hour attack in New York. Authorities said Akayed Ullah came to the U.S. in 2011 on a visa available to certain relatives of U.S. citizens. An earlier truck attack Oct. 31 on a bike path near the World Trade Center, authorities said, was carried out by an Uzbek immigrant.

Homeland Security Secretary Kirstjen Nielsen, the former deputy White House chief of staff confirmed last week by the Senate, said “while we are not aware of any specific credible threats today we are taking additional security precautions and assessing what other security enhancements” could be put in place.

Sessions called anew on Congress to strengthen immigration laws and said President Donald Trump’s administration was moving to more strictly enforce immigration law and reduce an immigration caseload that has tripled since fiscal 2009. Already, he said, the administration has hired 50 immigration judges since January and plans to hire 60 more in coming months to reduce a case backlog that has “overwhelmed” the immigration system.

He also said border crossings by undocumented immigrants are now at their lowest level in 45 years, vowing “that number can be zero.” And he signaled gangs such as the MS-13 with deep ties to Central America remain a prime Trump administration target amid its broader immigration crackdown.

Nielsen said law enforcement is redoubling efforts to sweep up members of MS-13, adding their violence will not be tolerated in U.S. communities. She described MS-13 as a “threat to our homeland security” and said members are “raping, killing and torturing Americans.”

“These savage criminals are in our communities and they are a deadly consequence of our unsecured borders and our failed immigration policies,” Nielsen said.

MS-13 members are suspected of particularly grisly slayings in Maryland, Virginia and New York — at least one of those attacks just miles (kilometers) from the nation’s capital. A hallmark of the gang is repeated slashes to a victim’s body.

In October, Sessions designated the gang as a “priority” for the Department of Justice’s Organized Crime Drug Enforcement Task Force. That designation directs prosecutors to pursue all legal avenues to target the gang and lets local police agencies tap into federal money to help pay for gang-related investigations.

While federal authorities say the threat from MS-13 has been increasing in the U.S., some experts who study gangs are skeptical.

Robert Brenneman, a sociologist at Saint Michael’s College in Vermont who has researched gangs in Central America, believes the threat posed by MS-13 in the U.S. has been exaggerated.

“Clearly, the MS-13 represents an opportunity for this administration to publicly herald his view of Central American undocumented youth as a menacing threat to the U.S.,” Brenneman said in an email.

MS-13, or the Mara Salvatrucha, is believed by federal prosecutors to have thousands of members nationwide, primarily immigrants from Central America. It emerged in the 1980s from a stronghold in Los Angeles. But its true rise began after members were deported back to El Salvador in the 1990s.

Sessions afterward told reporters he cast an absentee ballot in Tuesday’s special U.S. Senate election in Alabama but declined to specify who he voted for, citing “the sanctity of the ballot.” The winner takes the seat Sessions held before becoming attorney general.

“The people of Alabama are good and decent and wonderful people I’ve been proud to serve for 20 years in the Senate, and they’ll make the right decision, I’m sure,” Sessions said.

Republican Roy Moore, 70 — a twice ousted Alabama Supreme Court chief justice — is seeking a political resurrection amid accusations of sexual misconduct with teenage girls when he was in his 30s. His Democratic opponent, Doug Jones, 63, is a former U.S. attorney best known for prosecuting two Ku Klux Klansmen who killed four black girls in a 1963 church bombing.

Asked if he stood by comments last month to the House Judiciary Committee that he had “no reason to doubt” Moore’s female accusers, Sessions said: “I answered the question as I knew it at the time.”

Republicans hold a narrow 52-48 Senate majority. Alabama, a state where Trump remains popular, hasn’t elected a Democrat to the Senate since 1992.

(AP)