BBC: The head of the global nuclear watchdog has confirmed Iran is increasing its production of enriched uranium.
But International Atomic Energy Agency (IAEA) chief Yukiya Amano said it was not clear when they will reach a limit set under a 2015 international deal.
Iran announced last month that it would suspend some commitments in retaliation for sanctions reinstated by the US.
Mr Amano also said he was worried about the current tensions over the Iranian nuclear issue and called for dialogue.
Iranian Foreign Minister Mohammad Javad Zarif later said reducing tensions was only possible by stopping what he called the "economic war by America".
"Those who wage such wars cannot expect to remain safe," he told a news conference during a visit to Tehran by his German counterpart, Heiko Maas.
Mr Maas warned that the situation in the region was "highly explosive and extremely serious" and could lead to a military escalation between the US and Iran.