* Iran says has implemented agreed nuclear transparency steps * But IAEA seeks more information about detonators - sources * Iran says nuclear bomb allegations false; Reza Najafi, Iran's envoy to the International Atomic Energy Agency, made ** comment as he arrived shortly after 3 p.m. (1300 GMT) at the U.N. agency's Vienna headquarters for Monday's meeting with senior IAEA officials. Under a transparency and cooperation pact agreed between the two sides in **vember, Iran was to take seven practical measures by May 15 in a phased process to help allay international concern about its nuclear programme.