The peace conference gets its ceremonial start on Wednesday in the Swiss city of Montreux, and the open-ended negotiations begin on Friday in Geneva. Opponents of Iranian involvement say it would only undermine the talks. The opposition could follow through with its boycott threat — and even if it does attend, Iran’s presence could make it even more difficult to sell any potential agreements to the armed opposition inside Syria, much of which is already suspicious of the conference.

Some moderate rebel groups support the negotiations, but others, such as the powerful Islamic Front, have painted participation in them as treason.

The invitation also raised the question of what, if anything, Iran could do to help.

Iran has long pushed the idea that it can play an important role in attempts to bring the conflict — which has killed more than 130,000 people, many of them civilians, and displaced millions — to a negotiated end. In an interview with BuzzFeed earlier this month, one Iranian official suggested a key reason the country could make a difference in negotiations was its unique influence with Assad.

The official said that Iran had been “quite instrumental and helpful in persuading Syria to accept the chemical weapons deal” implemented this fall, in which Assad agreed to give up his stockpiles of the weapons to avoid a U.S. air strike. Iran, the official said, could play a similar role in Geneva. “They should invite the countries that have influence inside Syria and excluding Iran will not be helpful,” the official said, requesting anonymity because of the subject’s sensitivity.

“There are two realities inside Syria and we cannot dismiss any of them: the government and the opposition,” the official added. “The main matter for Iran is finding a political solution, based on the Syrian people’s will, and stopping the bloodshed as soon as possible.”