Heads of agencies shall assist the Department of State in its preparation of the Foreign Relations of the United States (FRUS) series by facilitating access to appropriate classified materials in their custody and by expediting declassification review of documents proposed for inclusion in the FRUS. If an agency fails to provide a final declassification review determination regarding a Department of State referral within 120 days of the date of the referral, or if applicable, within 120 days of the date of a High Level Panel decision, the Department of State, consistent with 22 U.S.C. 4353 and any implementing agency procedures, may seek the assistance of the Panel.