Zimbabwe's President Robert Mugabe has told his party's leaders that the power-sharing deal with the opposition is a "humiliation".
But he said the party had no alternative after losing the March parliamentary elections.
Mr Mugabe is expected to meet Prime Minister-designate Morgan Tsvangirai to discuss allocating ministerial posts under the deal.
Under the deal, Mr Mugabe's Zanu-PF has 15 posts in cabinet, Mr Tsvangirai's Movement for Democratic Change 13 and a smaller MDC faction three.
Meanwhile, the International Red Cross is to start distributing food aid shortly.
Red Cross spokesperson Matthew Cochrane said about 2 million people need food aid, and this could rise to 5 million - half the population - by the end of the year.
"The situation is critical," he said.
Mr Mugabe told a meeting of Zanu-PF's leadership: "If only we had not blundered in the March elections we wouldn't be facing this humiliation.
"This is what we have to deal with."
But he nevertheless said Zanu-PF remained "in the driving seat".
"We are still in a dominant position which will enable us to gather more strength as we move into the future," he said, according to the state-run Herald newspaper.
The deal is intended to share power equally but correspondents say it is unclear if either party has the upper hand.
Mr Mugabe will chair the cabinet, while Mr Tsvangirai will chair a "council of ministers" attended by all cabinet ministers.
The cabinet under Mr Mugabe will decide on government policy, while the council of ministers will implement it.
The new government's first priority is to try to revive the ruined economy.
Annual inflation is running at an official rate of 11m% and just one adult in five has a regular job.