london prime minister theresa may reaffirm britain commitment 2015 iran nuclear deal telephone conversation u.s. president donald trump ahead key u.s. decision whether tehran stick term pact trump cast doubt future joint comprehensive plan action jcpoa seek curb iran nuclear program return lift western economic sanction senior u.s. administration official say last week trump criticize pact embarrassment bad deal ever negotiate expect decertify iran compliance ahead oct. 15 deadline prime minister reaffirm uk strong commitment deal alongside european partner say vitally important regional security say statement may office follow call tuesday even prime minister stress important deal carefully monitor properly enforce contrast white house statement phone call say trump underscore need work together hold iranian regime accountable malign destabilize activities especially sponsorship terrorism development threaten missiles separate statement britain foreign office say iran uphold nuclear commitments add international pressure trump jeopardize security region nuclear deal crucial agreement neutralize iran nuclear threat foreign minister boris johnson say culmination 13 years painstaking diplomacy increase security region uk security implications continue encourage us consider johnson speak telephone u.s. secretary state rex tillerson iranian foreign minister javad zarif tuesday wednesday meet head iran nuclear agency london press continue compliance deal may trump also discuss need britain unite state others work together counter destabilize iranian activity region may office say britain unite state two eight signatories deal along iran china france russia germany european union china russia european state already express continue support deal iran say trump would able undermine pact trump decline certify iran compliance u.s. congressional leaders would 60 days decide whether reimpose sanction tehran suspend agreement early white house say trump would make announcement late week overall iran strategy include whether decertify nuclear deal may office say agree trump team remain contact ahead decision recertification uk reaffirm commitment iran nuclear deal call trump may 's office