Russia's foreign minister has described the UN decision to rescind its invitation to Iran to join this week's Syria peace talks in Geneva as a mistake, although not a catastrophe.

Sergey Lavrov said on Tuesday that the UN secretary general, Ban Ki-moon's decision to withdraw his last-minute offer to Iran to attend the conference would have a negative impact on the UN image.

Lavrov, speaking at a news conference, reaffirmed Russia's argument that the presence of Iran was essential for the success of the conference that is set to begin Wednesday in Montreux, Switzerland.

Ban retracted his invitation for Iran to attend the summit on Syria after Tehran said it did not support the June 2012 political transition deal that is the basis for the talks.

Diplomats had spent Tuesday trying to prevent the collapse of the largest international diplomatic effort to end the three-year conflict, with Iran refusing to concede that its last-minute invitation to attend meant it should endorse a transitional Syrian government – a move rejected by the Iran-backed Damascus regime.

Ban had belatedly invited Iran – a prominent supporter of Assad – on Sunday without first asking Tehran to agree to the principles of the earlier summit that had paved the way for the first direct talks between the Syrian opposition and government groups since the start of the conflict.

But the 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As soon as Iran's invitation was rescinded, Syria's opposition national coalition immediately confirmed its participation in the forthcoming talks, known as Geneva II.

"We appreciate the United Nations and Ban Ki-moon's understanding of our position. We think they have taken the right decision. Our participation is confirmed for 22 January," Monzer Akbik, chief of staff of the president of the National Coalition, told Reuters.

Another coalition member, Anas Abdah, said they would send a list of conference delegates to the UN later on Monday. The US hailed the withdrawal of the Iranian invite. US state department spokeswoman Jen Psaki said the US hoped "all parties can now return to focus on the task at hand, which is bringing an end to the suffering of the Syrian people and beginning a process toward a political transition". The secretary of state, John Kerry, is to attend the conference.

Ban's spokesman, Martin Nesirky, said that the secretary general "continues to urge Iran to join the global consensus behind the Geneva communiqué. 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".

After spending Monday trying to persuade Iran on the issue, Ban had released a statement saying he was dismayed by the failure of attempts ahead of the Geneva talks. "Iran, despite assurances provided orally to the secretary general, has made a disappointing public statement," his spokesman told reporters in New York. "The secretary general is urgently considering his options in light of the disappointing reaction of some participants."

Iran's endorsement of a transitional government would have implied a watering down of its support for the Assad regime, which has been its main ally in the Arab world for more than 30 years.

Close to 150,000 people have been killed, at least four million displaced, and the borders of Syria and its neighbours placed under immense strain.

Both Iran and Saudi Arabia have coveted a leading role in helping solve the Syrian crisis. Tehran has provided substantial funding and military support to Assad, while Riyadh has heavily backed rebel groups. Over the past year, the war has increasingly been a proxy campaign between the Iranians and the Saudis, with rising sectarian implications that spill well beyond Syria's borders.

As Geneva approached, both sides hardened their positions. Iran had said it would welcome an invitation, which it had attempted to frame through the prism of a recent rapprochement with the US and EU over its nuclear programme. Saudi Arabia had also wanted to play a prominent role in any detente, but only if Iran was absent.

There was no immediate response from the Iranian government. However, a senior advisor on foreign policy to Iran's supreme leader, Ali Khamenei, was quoted earlier in the evening as saying that Iran would not accept any precondition, referring to the principles set down at the Geneva I summit.

"The very negative point of the Geneva I statement is that it requires the Syrian legitimate government and the country's foreign-sponsored terrorists who have committed various crimes against Syrian people to sit on the same table and form a transitional government which means that at least half of this government will have to be terrorist supporters," said Ali-Akbar Velayati according to Iran's state Irna news agency.