State Department officials should enlist help from U.S. health agencies as they assess a series of mysterious attacks on American diplomats in Cuba, according to lawmakers frustrated with the pace of the investigation.

“We need to use all available resources to discover the medical cause and impact of what happened to our embassy personnel in Cuba,” House Foreign Affairs Chairman Ed Royce, R-Calif., and Democratic counterpart Eliot Engel of New York wrote in a Tuesday letter.