berlin germany worry u.s. president donald trump decide week iran respect two-year-old deal curb nuclear programme fear step worsen security situation middle east foreign minister sigmar gabriel say germany prepare work unite state change iran behaviour region want see agreement damage look great concern towards unite state gabriel tell reporters berlin urge white house call question important achievement improve security say reference 2015 accord reach trump predecessor barack obama seek detente tehran also offer help influence iran behaviour region germany ready price sacrifice nuclear deal trump expect decertify landmark agreement iran britain china france germany russia unite state european union despite advice senior members cabinet u.s. partner stick say iran respect deal u.s. congress would 60 days decide whether reimpose sanction lift exchange curb iran nuclear programme even congress take step deal could risk unravel washington tehran resort tit-for-tat retaliatory step u.n. nuclear watchdog repeatedly certify iran compliance deal term gabriel call accord great diplomatic success say prevent iran develop nuclear weapons head military conflict iran israel worry base signal come unite state president tell lawmakers nuclear deal iran fulfil gabriel say run counter view european countries participate deal well eu gabriel say make clear u.s. secretary state rex tillerson recent conversations europe due relative geographical proximity iran would see security interest damage nuclear deal collapse also draw attention signal step would send north korea big concern regard north korea unlikely north korean dictatorship would sign international agreement agree renounce nuclear weapons one agreement like iran call question gabriel say germany watch trump 's iran decision 'great concern