US President Donald Trump's administration said its creation of a new "national defense area" stretching more than 170 miles (270 kilometers) along the frontier would enable the army to support border patrols.

"It's their own autonomous decision and in their territory, but we hope it doesn't cross the border and that existing collaboration on security matters continues," Sheinbaum told a news conference.

"We don't know if it's to continue building the wall (along sections of the border) or what the objective is, but in any case, what we always ask for is respect and coordination," she added.

Trump last week signed a memorandum ordering federal land along the frontier to be made available to the Defense Department if needed to enable military activities including construction of border barriers.

"This new national defense area spans more than 170 miles across our border in New Mexico," White House Press Secretary Karoline Leavitt said Tuesday, adding that more than 90 miles would be added in Texas in coming weeks.

Leavitt said the move would allow US forces to better act against undocumented migrants, criminal gangs and "terrorists."

The troops would also work on stopping the smuggling of fentanyl and other narcotics, she said.

The land will be considered part of a military installation, enabling soldiers to exclude migrants from the area.

Since returning to office in January, Trump has deployed thousands more troops and two warships to beef up border security.