The head of the International Atomic Energy Agency is warning that the “space for negotiation and diplomacy ... is getting smaller” over Iran’s advancing atomic program as wars in the Mideast rage on and as President Donald Trump will return to the White House.

Rafael Grossi, head of the International Atomic Energy Agency, the U.N. nuclear watchdog, says the window of opportunity to diplomatically engage with Iran is beginning to "shrink."

U.N. atomic watchdog chief Rafael Grossi appealed to Iran's leadership on Tuesday to take steps to resolve longstanding issues with his agency a day before he arrives in the Iranian capital for crunch talks over its nuclear programme.

The head of the United Nations' nuclear watchdog will travel to Iran this week to meet with officials including its new president.