Nogales, Ariz. (Reuters) - U.S. Attorney General Jeff Sessions traveled to the U.S.-Mexico border on Tuesday to make his case for increased prosecutions of illegal immigrants, pressuring U.S. attorneys to prioritize cases against criminal migrants.

Sessions, a long-time proponent of tougher immigration enforcement, told U.S. Customs and Border Protection agents at the Port of Nogales, Arizona, that more illegal migrants should be prosecuted as criminals.

It is normally the role of the Secretary of Homeland Security to meet border agents. But Sessions made the visit to highlight his focus on enforcing federal laws as dozens of U.S. cities try to shield illegal immigrants from stepped-up prosecution and deportation efforts.

“Why are we doing this?” the former U.S. senator said. “Because it is what the duly enacted laws of the United States require.”

Sessions said that each U.S. attorney would be required to designate a point person on border security prosecutions by April 18. The person in that position, known as a border security coordinator, would be directed to coordinate with the Department of Homeland Security, according to Sessions’ memo.

The directive did not go beyond existing laws, but Sessions said his order “mandates the prioritizations of such enforcement” by U.S. attorneys.

The Trump administration has threatened to cut off U.S. Justice Department grants to so-called sanctuary cities that fail to assist federal immigration authorities.

Police in such cities have argued that targeting illegal migrants is an improper use of law enforcement resources. Sessions has said a failure to deport aliens convicted of criminal offenses puts whole communities at risk.

Under U.S. law, anyone who harbors or transports an undocumented immigrant, has crossed the border illegally two or more times, resists an immigration officer’s arrest or commits travel document fraud is subject to criminal prosecution.

Other immigrants apprehended for crossing the border illegally face civil procedures, with deportation the only penalty.

Sessions’ announcement was the latest move by the Trump administration to deter illegal immigration. President Donald Trump has also called for not releasing migrants with pending court cases, targeting more people in immigration raids and building a wall on the southwest border.

Speaking just 50 yards from a border fence on the Arizona-Mexico border, Sessions said that adding more fencing to the border will be a “force multiplier” against illegal migration.

He also said the Justice Department plans to add 50 more immigration judges in 2017 and 75 more in 2018. Immigration judges oversee civil immigration cases, but there is a backlog of over 540,000 pending cases due a shortage of judges.