The UN atomic agency's board of governors on Wednesday approved giving Japanese director general Yukiya Amano a new four-year term without even resorting to a vote, diplomats said.
In 2009, the International Atomic Energy Agency's 35-member board had needed six rounds of voting to select Amano for his first term, with developing countries worried he would be too pro-Western.
This time however the 65-year-old's second term, which will start in December following approval from all 159 IAEA members in September -- a formality -- passed by consensus, meaning no vote was taken.
Amano's highest-profile challenge in his second term will again be Iran, amid international concerns that Tehran wants to develop nuclear weapons under the guise of a civilian atomic programme.
Iran says that as a signatory to the Non-Proliferation Treaty, which aims to prevent the spread of nuclear weapons and to get nuclear-armed states to disarm, it has the right to a civilian nuclear programme.
But the IAEA, which conducts regular inspections of Iran's facilities, says that because of a lack of cooperation it is "unable to... conclude that all nuclear material in Iran is in peaceful activities".
As a result, the UN Security Council has passed six resolutions calling on Iran to suspend parts of its programme until its purely peaceful nature can be confirmed. Israel and the United States have also refused to rule out military action.
In addition, the IAEA wants Tehran to address what it suspects are indications that the programme also has -- or at least had in the past -- "possible military dimensions" aimed at developing the bomb.
Stretching back more than a year, the IAEA has held a series of failed meetings pressing Iran to address these allegations by giving the agency access to sites, documents and scientists, the latest last month.
Iran says the IAEA's claims, set out in a major report in November 2011, are based on information from Israeli and Western spy agencies -- information that it has not been shown -- and that it has never sought to develop nuclear weapons.
The Vienna-based IAEA, founded in 1957, also aims to promote the peaceful uses of nuclear technology including energy.