The Secretary of State is authorized, notwithstanding any other provision of law and subject to the conditions provided in this section and section 277d-11 of this title, to enter into an agreement with the appropriate official or officials of the United Mexican States for the operation and maintenance by the International Boundary and Water Commission, United States and Mexico, of the Nogales sanitation project, located at Nogales, Arizona, and Nogales, Sonora, Mexico, heretofore constructed by the said Commission, which agreement shall contain such provisions relating to a division between the two Governments of the costs of such operation and maintenance, or of the work involved therein, as may be recommended by said Commission and approved by the Government of Mexico and by the Secretary of State on behalf of the Government of the United States: Provided, That no such agreement shall be entered into until the governing body of the city of Nogales, Arizona, has given assurances satisfactory to the Secretary of State that it will, so long as such agreement remains in force, contribute an equitable proportion, as determined by the United States section of said Commission, subject to the approval of the Secretary of State, of the costs of such operation and maintenance allocated to the United States.