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.

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.

"I am deeply grateful for the trust that the board of governors placed in me once again," Amano told reporters.

"The challenges are many and huge ... I like my job and enjoy my job, and I am very happy to do good in the world and make a difference."

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 further nuclear disarmament, 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.

On Iran, a new chief inspector, Tero Varjoranta of Finland, is due to start in October, replacing retiring Belgian Herman Nackaerts -- described in leaked US cables as "not bad".

The Vienna-based IAEA, founded in 1957, also aims to promote the peaceful uses of nuclear technology including energy.

In the eyes of many developing countries in 2009, Amano's good points included his undisputed expertise in nuclear matters and the fact that he came from the only country to have been bombed with a nuclear device.

But on the negative side, succeeding Egyptian Mohammed ElBaradei, who had frequently clashed with Washington, most notably over Iraq, he was seen as a potential Western puppet bent on eroding the IAEA's impartiality.

This impression was heightened by the release by WikiLeaks of 2009 US diplomatic cables saying Amano was "solidly in the US court on every key strategic decision, from high-level personnel appointments to the handling of Iran's alleged nuclear weapons programme."

But according to Mark Hibbs, a seasoned IAEA-watcher at the Carnegie Endowment for International Peace, Amano has managed to soothe developing countries' concerns, while also doing exactly the job that Western nations wanted.

"He not only succeeded in the sense that he carried out the agenda which his supported countries on the board wanted him to do, but at the same time he also overcame the challenge of facing angry and disappointed, disgruntled developing countries," Hibbs told AFP.

"I think that the two groups, the North group and the South group, are probably in principle not closer together than four years ago. But a truce that has emerged -- in part because of Amano's efforts."