Belgium, Bulgaria, Cyprus, Denmark, Hungary, Ireland, Italy, the Netherlands, Poland, Portugal, Romania, Slovenia and Slovakia sent charges d'affaires - acting heads of mission when the ambassador is away.

Only Germany and Austria stood out by sending lower rank representatives.

The EU last month criticised Iran's violent crackdown on opposition protesters and threatened to pull out its ambassadors after the arrest of nine British diplomats.

But it has steered clear of questioning the legitimacy of the election to avoid accusations of outside interference.

The EU presence at the inauguration event stands in contrast to the actions of moderate Iranian politicians such as Mohammad Khatami and Ali Akbar Hashemi Rafsanjani, who stayed away in protest.

Opposition leader Hossein Musavi and around 70 other MPs were also absent.

"This was an excellent opportunity for Sweden, as current holder of the EU presidency, to show solidarity with the people who have been fighting for free and fair elections in Iran, and that chance was wasted," Urban Ahlin, a spokesman for Sweden's opposition Social Democratic party, said on Swedish radio.

Swedish foreign minister Carl Bildt wrote in his blog that diplomats need to work with countries such as Iran or North Korea, citing Swedish support in recently helping to free two US journalists held in the Asian country.

"It is clearly better to be present than to be absent," he said.

"Participation in an official ceremony [the Ahmadinejad inauguration] does not mean that we support this government or its actions. As the [EU] presidency, it's important to keep open our channels of communication," Swedish foreign ministry spokesman, Anders Jorle, told this website.

The British foreign office in a statement described its decision to attend as "hard-headed diplomacy."

"We have not sent a message of congratulations to president Ahmadinejad. But ...communication channels have to be kept open," it also said.