Zimbabwean Finance Minister Tendai Biti said on Saturday the southern African country would struggle to afford the two votes - a referendum and an election - which are due to be held this year in the space of a few months.
Biti, who is also secretary-general of the Movement for Democratic Change (MDC), said the referendum would cost $85 million (56 million pounds) and these funds were not available from Zimbabwe's 2013 budget of $4 billion.
"Clearly Zimbabwe doesn't have sufficient funds to hold both the referendum and the election. More so when these two important events are following so closely after the national census we had done in August and September," Biti told reporters ahead of an MDC rally in the South African city of Pretoria.
The MDC party is headed by Morgan Tsvangirai who went into government with his rival President Robert Mugabe after a violent and disputed vote in 2008.
Zimbabwe will ask its citizens to decide on a new constitution in a referendum on March 16 and adoption of the document would pave the way for elections in July, potentially ending Mugabe's 33-year run as president.
"We expect the international community will come to our assistance. We are also trying to mobilise resources from the domestic economy using various instruments including treasury bills, bonds and so forth," said Biti of the country's attempts to raise the money it needs to go to the polls.
But the plan to seek funding for the votes from foreign donors or the private sector could be a hard sell. Western governments have questioned human rights abuses in the country and businesses like platinum producer Zimplats are wary of rapidly-changing policies that threaten profitability.
As leaders of the fragile power-sharing government, Mugabe and Tsvangirai have agreed on the terms of a new constitution to strengthen the powers of parliament and curb those of the president.
Tsvangirai, who accuses Mugabe of using violence to cling to power, has promised to fix an economy analysts say has been ruined by controversial policies such as the seizure of commercial farms to resettle landless local people.
"The 2013 election is without a doubt easily the most important election after the 1980 election in our country. It's a make-or-break election," said Biti, who was in Pretoria to rally support for the MDC among Zimbabweans living in South Africa.
The party believes the two million or so Zimbabweans living in neighbouring South Africa have a pivotal role to play in the election and is encouraging them to return home to vote.
(Reporting by Sherilee Lakmidas; Editing by Rosalind Russell)