The United States will rejoin UNESCO after an 18 year absence. US President George W. Bush made the announcement at the UN General Assembly on 12 September. In a letter sent to UNESCO staff, Koichiro Matsuura, secretary-general of UNESCO, noted that the "return of the United States considerably bolsters our endeavours" in "promoting universal values and facing universal challenges." Matsuura expressed his appreciation to staff for the part they "are playing in the revitalization of UNESCO." UNESCO serves as ICTP's lead administrative agency.