The UN made the decision after the invitation angered the US and the Western-backed Syrian opposition.

The peace conference, due to begin on Wednesday, is the biggest diplomatic effort to end the three-year conflict.

More than 100,000 people have been killed and millions more displaced in the war.

The Syrian government and the main exiled opposition group, the National Coalition, are due to send delegates to the conference, which begins in the Swiss town of Montreux.

The so-called Syrian National Coalition had threatened to pull out if the invitation to Iran was not rescinded, but they have since confirmed that they will now be attending.

UN chief Ban Ki-moon had invited Iran after speaking in private to senior Iranian officials, who had assured him that they "understood and supported the basis and goal of the conference," UN spokesman Martin Nesirky said.

Nesirky said: "Given that it has chosen to remain outside that basic understanding, he has decided that the one-day Montreux gathering will proceed without Iran's participation."

It is unclear whether Iran will be able to join the talks two days later, when they move to Geneva.

US officials welcomed the withdrawal, saying they hoped the focus could return to the content of the talks.

BA/BA