18 U.S.C. § 2337: Suits against Government officials

No action shall be maintained under section 2333 of this title against—(1) the United States, an agency of the United States, or an officer or employee of the United States or any agency thereof acting within his or her official capacity or under color of legal authority; or (2) a foreign state, an agency of a foreign state, or an officer or employee of a foreign state or an agency thereof acting within his or her official capacity or under color of legal authority.