* IAEA chief Amano has taken "firm" line towards Iran
* Criticised over initial response to Fukushima disaster
* Diplomats expect new term for veteran Japanese diplomat
VIENNA, Sept 26 (Reuters) - United Nations nuclear agency chief Yukiya Amano, a key figure in international diplomacy over Iran's disputed nuclear activity, will seek a new four-year term next year, the Vienna-based organisation said on Wednesday.
Western diplomats say they expect Amano, who has taken a tougher approach on the Iran nuclear file than his predecessor Mohamed ElBaradei, to be reappointed without problems, in contrast to his close election victory in 2009.
"I don't expect anyone will challenge him," one European diplomat said, adding that Amano has been "very firm" on Iran.
The 35-nation governing board of the International Atomic Energy Agency (IAEA), which will decide on the issue by June next year, on Monday set a Dec. 31 deadline for the nomination of candidates. So far, Amano is the only confirmed candidate.
"The DG (Director General Amano) has announced that he is available for another term," the IAEA's press office said in an e-mail on Wednesday.
Under Amano, the IAEA was criticised last year for a perceived slow initial response to Japan's Fukushima nuclear disaster and the agency's ties with Tehran have become increasingly strained.
However, Western diplomats are generally happy with the way Amano has stepped up pressure on Iran to make it stop stonewalling an agency investigation into suspected atom bomb research, even if that push has yet to bear fruit. Iran denies Western allegations that it is seeking to develop nuclear weapons capability.
In 2009, supported largely by industrialised nations, Amano defeated South Africa's Abdul Samad Minty in a sixth round of balloting after five inconclusive votes.