The attorney general is hereby empowered, authorized, and directed to retain attorneys to take exclusive charge of prosecuting, collecting, and recovering from the United States any such claim which may be developed, and to prosecute, at their own expense, any claim before such tribunal of the government as may be deemed best for the interests of the state, detailed reports to be made, from time to time and whenever requested by the attorney general, of the progress of prosecution of any claim; provided, that no composition of any claim shall be concluded without the written approval of the attorney general.