"If the deal fails we will remain a pariah," Makoni told reporters,
Makoni quit President Robert Mugabe’s ruling party to contest the presidential polls in March as an independent candidate. In the first round vote, he landed third behind opposition leader Morgan Tsvangirai and Mugabe.
Zimbabwe was then forced into a June runoff plagued by political violence and Tsvangirai pulled out of the race.
Four weeks ago, Mugabe and Tsvangirai reached a power-sharing deal to form a unity government. Makoni was left out of the agreement, which is already faltering after Mugabe claimed the most important cabinet posts for his party.
"Since the deal was signed, the suffering of the people has actually become worse," Makoni said, announcing plans to form a new opposition party.
"The people are suffering immensely, they are angry and frustrated and they feel hostage to leaders who seem uncaring and insensitive to their plight. We share the people’s anger and frustrated," he said.
"We wonder what compelled the leaders to sign an incomplete agreement, if there are major issues unresolved. They raised the people’s hopes and expectations, whetted the national appetite for progress, only to dash the hopes and expectations," he added.
South Africa’s former president Thabo Mbeki, who brokered the power-sharing deal, was expected in Harare late Monday to try to save the plans for a unity government. – Sapa-AFP