SAN ANTONIO (AP) — A top health official has voiced concern that too little money is available to house the unexpectedly high numbers of unaccompanied children crossing the U.S.-Mexico Border.

In a letter obtained by the Associated Press, Health and Human Services Secretary Sylvia Burwell told members of Congress' appropriations committee Friday that the agency "may face serious funding challenges in meeting the costs of accommodating the increased number of children."

The secretary says the agency hopes to avoid the situation it faced in the summer of 2014 when tens of thousands of children and families overcrowded Border Patrol shelters.

Messages left with the agency's spokesman were not immediately returned.

A total of 10,588 unaccompanied children crossed the border in October and November, prompting the agency to open new shelters in Texas and California.