NEW YORK (Reuters) – Oil prices firmed on Monday on tensions over Iran’s nuclear program but gains were capped by concerns about global economic growth and consequently oil demand. Iran on Monday threatened to restart deactivated centrifuges and step up its enrichment of uranium to 20% in a move that further threatens the 2015 nuclear agreement that Washington abandoned last year. Washington has imposed sanctions that eliminate benefits Iran was meant to receive in return for agreeing to curbs on its nuclear program under the 2015 deal with world powers. The confrontation has brought the United States and Iran close to conflict, with U.S. President Donald Trump calling off air strikes last month minutes before impact. On Sunday, Trump issued another warning over Iran’s nuclear activities. “They’d better be careful,” he said. Iran’s Oil Minister Bijan Zanganeh said on Sunday that he was very hopeful of an improvement in the country’s crude exports, state TV reported. “We see enough possibility of military conflict to cushion renewed price declines that might be driven by mounting expectations for a major slowing in the global economic growth path,” Jim Ritterbusch of Ritterbusch and Associates said in a note.