PRAGUE (AP) — U.S. Defense Secretary Jim Mattis says the military has already begun delivering jersey barriers to the southern border in conjunction with plans to deploy active duty troops there as a caravan of Central Americans slowly heads across Mexico toward the United States.

Mattis says details of the deployment, including the number of troops, are still being worked out, but he should have them by Sunday night.

The additional troops will provide logistical and other support to the Border Patrol and will bolster the efforts of the approximately 2,000 National Guard forces already there. The new forces are expected to provide logistical assistance such as air support and equipment, such as vehicles and tents.

Mattis spoke Sunday during a visit to the Czech Republic.