By Sadeq Saba
BBC regional analyst
Iran's former parliamentary speaker Mehdi Karrubi has said he will stand as a reformist candidate in presidential elections in June.
Karrubi is unlikely to win the support of those after radical change
Mr Karrubi's candidacy means that the reformist camp is now officially split.
Several prominent reformist and conservative candidates have put their names forward to replace President Mohammad Khatami.
But the country's influential former president, Akbar Hashemi-Rafsanjani, remains undecided.
With six months to go before Iran's presidential elections, a flurry of activity has already begun.
Mr Khatami is barred by the constitution from standing again after serving two terms in office.
Mr Karrubi is known as a compromising, moderate reformist who remains loyal to the clerical establishment. It is unlikely that Iran's young population who wants radical changes will support him.
The country's largest reformist party, the Participation Front, had already chosen the former education minister, Mostafa Moin, as its candidate.
He is more popular with students. He resigned from his post in President Khatami's cabinet in 2003 in protest at conservative policies.
But reformers fear the hardline constitutional watchdog, the Guardian Council, may disqualify him.
Even before this split, the reformers did not have much chance to do well in the poll because of the mass disenchantment of the voters with their failure to deliver on their promises of more freedoms.
The conservatives have their own difficulties and have failed so far to agree on a single candidate.
Several conservatives, including the former foreign minister, Ali-Akbar Velayati, and the former head of state broadcasting, Ali Larijani, have announced their candidacy.
And Mr Rafsanjani, who is known as a pragmatic conservative, could change many calculations if he decides to enter the race.
But whoever succeeds President Khatami faces huge challenges - including the task of convincing the international community that the Islamic Republic's nuclear programme is peaceful.