The Title 42 program, introduced under president Donald Trump to use pandemic measures to expel people crossing without migration documents, will end on May 11.

With the easing of coronavirus regulations -- including Monday's decision to lift vaccination requirements for inward travelers -- President Joe Biden's administration can no longer apply Title 42 for border controls.

"For 90 days, these 1,500 military personnel will fill critical capability gaps, such as ground-based detection and monitoring, data entry, and warehouse support," spokesman Brigadier General Pat Ryder said in a statement.

The deployment will add to 2,500 troops already assisting the US Border Patrol and other agencies poised for the long-forecast jump in border crossers.

The Department of Homeland Security stressed that the military personnel will not be involved in law enforcement, but instead will help in backup activities like border monitoring, IT services and warehouse support.

"This support will free up DHS law enforcement personnel to perform their critical law enforcement missions," the department said in a statement.

On February 21 the Biden administration announced a new set of restrictions aiming to penalize people who cross into the country illegally.

They will have to first go through the process of applying online through a Customs and Border Patrol (CBP) app, or to apply first for asylum in one of the countries they pass through to get to the US border.

In addition, last week the State Department announced it plans to set up processing centers for hopeful migrants in other countries -- starting with Colombia and Guatemala.

Canada and Spain have also agreed to take in some of those who cleared by the processing centers to emigrate, US officials said.

"It's an approach focused on making migration more safe, orderly and humane and advancing the interests of the American people," Secretary of State Antony Blinken said.