WASHINGTON (AP) — The Obama administration on Friday urged calm over the single case of Ebola in the United States, seeking to reassure the American public that there is little chance of an outbreak of the illness in this country. The Pentagon said it had begun the long-awaited aid to disease-ravaged Liberia, with medical testing at two new labs and construction of treatment centers.

The administration has long contended that the best way to contain Ebola is to attack it at its source. The Pentagon’s spokesman said Friday that up to 4,000 troops could be deployed to West Africa, a number that has been slowly climbing as military leaders arrive and assess the need.