By Humeyra Pamuk, Dave Graham and Nandita Bose BUERGENSTOCK, Switzerland/WASHINGTON, June 23 (Reuters) - The United States waived sanctions on Iran for 60 days from Monday after the first talks under a nascent peace deal, with U.S. President Donald Trump saying he will "do what I have to do" if Iran does not stick to its side of the agreement. U.S.