A fourth day of power-sharing talks has begun in Zimbabwe, with President Robert Mugabe appearing optimistic and the opposition cautious.
"It's a day for deals," Mr Mugabe said as he arrived for the talks.
But an opposition spokesman has reportedly called for the UN and African Union to help break an impasse.
The US has threatened to impose new sanctions on Mr Mugabe if he does not agree to share key posts with the opposition, AFP news agency reports.
Former South African President Thabo Mbeki is hosting the crisis talks in Harare.
The BBC's Jonah Fisher in Johannesburg says earlier rounds of talks were given impetus by Mr Mbeki's need to return to his presidential duties in South Africa.
Now removed from office, Mr Mbeki's diary is clear and his ability to seal a deal once again open to question, our correspondent says.
When Morgan Tsvangirai, leader of the opposition Movement for Democratic Change, arrived for the talks on Friday he sounded cautious saying, "We all have to have hope don't we?"
President Mugabe last week allocated the most important cabinet posts to his Zanu-PF party, prompting Mr Tsvangirai to threaten to pull out of a deal to share power.
The rivals signed the deal last month, under which Mr Tsvangirai would become prime minister, but they did not thrash out which party would hold which posts.
"We have reached a deadlock on all issues," said opposition spokesman Nelson Chamisa as talks ended on Thursday.
"They [the UN and AU] are the guarantors of the agreement. If Zanu-PF continues to be intransigent, then those institutions should step in," he told Reuters news agency before talks resumed on Friday.
Reports suggest that Mr Mugabe may have agreed to let the MDC take the key finance post on Thursday.
But they could not agree on home affairs, sources say.
Zanu-PF officials have accused the MDC of intransigence, state media reports.
"I would not want to call the delay dilly-dallying, but we have made a lot of compromises. Everyone has made some compromises and we hope that this will be all concluded tomorrow [Friday]," the state-owned Herald newspaper quotes Mr Mugabe as saying after talks ended on Thursday.
Meanwhile, the top US diplomat for Africa, Jendayi Frazer has said she is disappointed by the lack of progress.
"Right now we're not so optimistic. It doesn't look very good for power-sharing," she said, according to the AFP news agency.
"If it doesn't work then we are going to continue the pressure that we've put on the government. We will look at new sanctions against President Mugabe and his regime."
On Wednesday, Mr Mugabe and MDC secretary general Tendai Biti had both said they hoped a deal could be reached on Thursday.
Mr Mugabe had earlier allocated the main ministries, including defence, home, foreign affairs, and justice, to his Zanu-PF party.
Mr Tsvangirai wants 10 cabinet positions to be revisited in discussions with Mr Mbeki.
But Zanu-PF says only one ministry - finance - is up for discussion.
According to the original deal - which allocates 15 ministries to Zanu-PF, 13 to the MDC and three to a smaller MDC faction - only Zanu-PF has a ministerial seat vacant.
Finance is one of the most crucial posts, as Zimbabweans hope the power-sharing deal will lead to action to tackle the economic crisis.
Donors have promised to help finance a recovery plan but they are unlikely to release funds if a Zanu-PF minister is in charge of the economy.
At 231,000,000%, Zimbabwe has the world's highest rate of annual inflation, while some two million people need food aid.
Aid agencies warn that figure could double, leaving almost half the population going hungry within the next few months.
As well as finance, the MDC also insists it should have home affairs - and control of the police - if Zanu-PF has defence.
The MDC has accused both the police and the military of taking part in violent attacks on its supporters ahead of the presidential run-off in June.