The Pentagon says Defense Secretary Jim Mattis has approved plans to extend the deployment of active-duty U.S. troops at the southern border with Mexico until January 31.

The 45-day extension was requested by the Department of Homeland Security. It involves military forces that will install and repair wire barriers and provide security and transportation for border patrol agents. The troops are spread across California, Arizona and Texas.

Officials have said the number of troops will drop from about 5,400 now to roughly 4,000. The officials spoke anonymously to describe internal deliberations.

President Donald Trump ordered the deployment of active-duty troops to the border in response to a caravan of Central American migrants walking north toward the U.S. Critics dismissed the deployment as a political stunt ahead of the midterm elections.