UNITED NATIONS  - Under huge pressure from the United States, Secretary-General Ban Ki-moon, has retracted his invitation for Iran to attend Wednesday's peace conference on Syria, after Tehran said it did not support the June 2012 political transition deal that is the basis for the talks.

Although the withdrawal of the invitation, which evoked strong objections from the United States and Syrian opposition, prevented the collapse of the conference, the absence of Iran, a major player in the region, is likely to complicate efforts towards resolving the conflict, now in its third year. Iran, which received the invitation on Sunday, refused to concede that to attend the conference meant it should endorse a transitional Syrian government, a moved rejected by Iranian-backed Damascus regime.

Ban last minute invitation enraged the US, Britain and the main Syrian opposition body, which warned it would not turn up in the Swiss town of Montreux unless Iran conceded on the issue of a transitional government - a central pillar of western-backed diplomatic moves to oust President Bashar al-Assad. As soon as Iran's invitation was rescinded, Syria's opposition national coalition immediately confirmed its participation in the forthcoming talks, known as Geneva II.

Announcing the withdrawal of the invitation, the secretary-general's spokesman said Ban was "deeply disappointed" by public statements on Monday from Iran, a close ally of President Assad.

"He (Ban) continues to urge Iran to join the global  consensus behind the Geneva communique," Spokesman pokesman Martin Nesirky said.  "Given that it has chosen to remain outside that basic understanding, (Ban) has  decided that the one-day Montreux gathering will proceed without Iran's participation."

The UN chief announced Sunday night that he had invited Iran to attend the conference’s opening on Wednesday after Foreign Minister Javad Zarif assured him that his country understands that the basis of the talks is full implementation of an action plan adopted in the so-called Geneva Communique of 2012.

“The Secretary-General is deeply disappointed by Iranian public statements today that are not at all consistent with that stated commitment,” Nesirky said.

A statement issued by Iran's Mission to the United Nations said Iran does not accept any preconditions. "If the participation of Iran is conditioned to accept Geneva I communique, Iran will not participate in Geneva II conference."

AFP adds: Iran on Tuesday slammed the United Nations for withdrawing Tehran's invitation to a peace conference on Syria and said UN chief Ban Ki-moon had bowed to outside pressure. "We regret that Secretary General Ban Ki-moon has withdrawn the invitation under pressure," Foreign Minister Mohammad Javad Zarif told reporters, ISNA news agency reported. "It is also regretful that Mr Ban does not have the courage to provide the real reasons for the withdrawal," he said. "This behaviour is beneath the dignity of the UN's secretary general." After strong objections from the United States and the Syrian opposition, Ban on Monday withdrew his invitation to Iran, the Damascus regime's main regional ally, less than 24 hours after it was issued.

Meanwhile, Former international prosecutors said Tuesday they have evidence from a defector proving that the regime of Assad has systematically killed and tortured around 11,000 people.

A report by three top investigators commissioned by Qatar, which backs the Syrian rebels, examined thousands of pictures said to have been smuggled out by a former military police photographer.

The report shows evidence of starvation, strangulation and beatings, and features pictures of emaciated corpses with livid wounds.

The release came a day before talks were due to begin in Geneva aimed at negotiating an end to Syria's bloody civil war. Syria denies torturing detainees.