Former finance minister Simba Makoni, a senior member of ZANU-PF, entered the presidential race on Tuesday, in the first major challenge to Mugabe from within the ruling party in 20 years.

He had been expected to register for the poll on Friday but Zimbabwe authorities moved the nomination date to February 15 after some politicians won a court order to delay the process.

On Wednesday, Zimbabwe's government-controlled media branded Makoni a British and American-sponsored puppet seeking to split ZANU-PF and oust Mugabe.

Joseph Chinotimba, deputy leader of the war veterans, was quoted as saying that Makoni was a political turncoat who would suffer a humiliating defeat in the March 29 general election.

"We are now going to campaign vigorously for President Mugabe. I feel sorry for Makoni, he has lost the political plot," Chinotimba told the Herald newspaper.

"From today to the nomination date we will have finished with them. Traitors should know that ZANU-PF has a history of dealing harshly with their kind," he said.

Chinotimba said Mugabe's war veteran supporters -- who have anchored Mugabe's election campaigns since 2000 -- would not allow Makoni and his supporters to enter the party's offices.

"We are calling on all war veterans to take control of the party," he said.

War veterans, who fought in the 1970s conflict, along with members of ZANU-PF, have turned violent in the past in support of Mugabe. There are 30,000 war veterans in Zimbabwe.

Makoni will run as an independent because, according to ZANU-PF rules, he will be automatically expelled from the party.

Political analysts say Makoni is popular with the business community and urban voters disenchanted with Mugabe and the main opposition Movement for Democratic Change (MDC) but doubt he has the muscle to defeat the veteran Zimbabwean leader.

Zimbabwe's privately owned media has reported that Makoni is backed by a faction led by retired army general and member of the ruling ZANU-PF party's top decision-making body, Solomon Mujuru. Mujuru is married to Vice President Joyce Mujuru.

Makoni said he had consulted party members and activists across Zimbabwe before deciding to run. Despite economic turmoil, 83-year-old Mugabe had been expected to defeat the divided opposition in the election.

Analysts say shortages of food, foreign currency and fuel, and the world's highest inflation rate -- officially pegged at 26,000 percent -- are the biggest challenge to Mugabe's rule.

But the opposition has failed to capitalise on Mugabe's failure to ease the crisis and it remains to be seen if daily hardships will push Zimbabweans to support Makoni.