Grossi's appointment for four more years still has to be approved by all 176 members of the International Atomic Energy Agency (IAEA) at its annual meeting in September but this is seen as a formality.

"I'm deeply honoured by the board's unanimous decision to appoint me for another term in office, and very grateful for the confidence and trust member states continue to place in me," the 62-year-old career diplomat said.

"It comes at a time when we face many major challenges," Grossi said of his turbulent first term, whch was marked by crises from Russia's war on Ukraine, to Iran and North Korea.

In December 2019, Grossi became the first IAEA head to hail from Latin America, following the death in office of the former director general, Japanese career diplomat Yukiya Amano.

The polyglot Argentinian father of eight, who is known for his dynamic and outspoken manner, last year visited Ukraine's Zaporizhzhia nuclear plant -- Europe's largest -- in an effort to establish a security zone around the site, which has been subject to frequent shelling.

On Thursday, Grossi again warned of the danger of repeated electricity outages at the Zaporizhzhia plant, after a new missile strike left it running on diesel generators.

Navigating the IAEA's role in the supremely complex and sensitive Iranian nuclear dossier has been another challenge for Grossi.

In 2015, the UN watchdog was tasked with monitoring the implementation of the landmark nuclear deal, which was concluded between Tehran and world powers and was designed to curb Iran's nuclear programme in exchange for sanctions relief.

The deal collapsed after Washington withdrew unilaterally in 2018 under then president Donald Trump and efforts to revive it have since stalled.

"The DG (Grossi) has shown extraordinary leadership during some of the Agency's most significant & historic challenges," Laura Holgate, United States ambassador to the United Nations in Vienna, wrote on Twitter.