A senior member of Zimbabwe's ruling party has said he will challenge President Robert Mugabe in 29 March polls as an independent candidate.
Simba Makoni could appeal to Zanu-PF and opposition supporters
"I offer myself as candidate for the office of president," former finance minister Simba Makoni told reporters.
He is seen as coming from the moderate wing of the Zanu-PF but does not have a strong grass-roots support base.
The two opposition Movement for Democratic Change factions are each fielding candidates in the election.
In its December congress, Zanu-PF endorsed Mr Mugabe as its presidential candidate in the 29 March election, despite speculation that he would face a challenge from within his party.
Other senior party officials than Mr Makoni had been seen as Mr Mugabe's most likely challengers, but none of them has challenged Zimbabwe's long-time leader in public.
Mr Makoni, 57, said he would have liked to contest the election on behalf of Zanu-PF but also blamed its leaders for Zimbabwe's economic crisis.
"I share the agony and anguish of all citizens over the extreme hardships that we all have endured for nearly 10 years now," he said.
1980: Named deputy minister aged 30
2002: Sacked as finance minister after argument with Mugabe
2002: Went to South Africa
Possible support of Zanu-PF heavyweight Solomon Mujuru
"I also share the widely held view that these hardships are a result of failure of national leadership and that change at that level is a pre-requisite for change at other levels of national endeavour."
The BBC's Peter Greste says Mr Makoni could pose a stronger challenge to President Mugabe than the divided opposition.
But our correspondent notes the former finance minister is standing as an independent and so will not have access to any of the resources of the ruling party or the state to help his campaign.
He is believed to have the backing of Zanu-PF heavyweight Solomon Mujuru, whose wife Joyce is vice-president.
Zimbabwean political analyst John Makumbe told the BBC that Mr Makoni's candidature was a "significant development".
"It will split the Zanu-PF, Mugabe vote," he said, especially if he does indeed have Mr Mujuru's backing.
MDC MP Priscilla Misihairabwi Mushonga said Mr Makoni was very courageous to publicly challenge Mr Mugabe.
"There is a lot of excitement about this," she said.
Mr Makoni has been mentioned as a possible compromise candidate between different Zanu-PF factions and even the opposition for many years.
After 18 months as finance minister, he was sacked in 2002 over policy differences with Mr Mugabe.
Mr Makoni is seen as a reformer and a moderate
The MDC had insisted on a new constitution before the elections, as well as guarantees they would be free and fair.
Previous polls have been characterised by violence and allegations of fraud.
Zimbabwe has the world's highest annual rate of inflation - 26,000% - and only an estimated one adult in five has a job.
Mr Mugabe's critics blame the economic crisis on his policies, especially the seizure of white-owned farms.
He blames a western plot to bring him down.