The United States, intensifying pressure on Damascus, moved Thursday to financially clamp down on three Syrian institutions suspected of helping spread weapons of mass destruction. The Treasury Department's action means that any bank accounts or financial assets belonging to the three entities found in the United States would be frozen. Americans also are prohibited from doing business with them. The three entities targeted are the Higher Institute of Applied Science and Technology, the Electronics Institute and the National Standards and Calibration Laboratory. "Syria is using official government organizations to develop nonconventional weapons and the missiles to deliver them," Stuart Levey, Treasury's under secretary for terrorism and financial intelligence, said in explaining the United States' action.