Washington, Jan 15 (IANS): The deployment of active-duty US troops at the border with Mexico will most likely be extended through September, the Pentagon has announced.

Prior to Monday's announcement, Pentagon's border mission had previously been scheduled to end on December 15, and the Defence Department later extended the deployment into January, reports The New York Times.

The Pentagon said that its "assistance" would continue through September 30 at the Department of Homeland Security's request, and that the support would focus on "mobile surveillance and detection" and placing concertina wire "between ports of entry".

It was not immediately clear exactly how many troops are currently at the border or how the number is expected to change.

The Pentagon did not disclose any more details.

In a rare use of military force first announced in October, President Donald Trump's administration sent about 5,900 active-duty troops to join Border Patrol agents and National Guard members, as a caravan of Central American migrants made its way toward the US.

The extension comes as a new migrant caravan was forming in Honduras and also during the longest shutdown of the federal government in American history that entered its 24th day on Monday.

Trump continues to push for a wall to stem what he calls a crisis at the border.