Zimbabwe police said they arrested people for obstruction
More than 50 Zimbabwean opposition supporters have been arrested after staging a strike, the party says.
Police have accused the Movement for Democratic Change (MDC) of trying to incite violence with their strike call, in protest at delayed poll results.
But a coalition of Zimbabwean doctors said its members had seen and treated more than 150 people who had been beaten and tortured since the polls.
International concern has been raised at a UN Security Council session.
The special meeting, called by South Africa's leader Thabo Mbeki, was supposed to be about how the UN can work with the African Union to bring peace to the Africa's conflicts, from Somalia to Sudan's Darfur region.
But leaders have used the opportunity to address the Zimbabwe issue.
No-one thinks - having seen the results at polling stations - that President Mugabe has won this election
UN Secretary General Ban Ki-moon said the absence of a transparent solution to the impasse could mean the "situation could deteriorate further, with the serious implications for the people of Zimbabwe".
"The international community continues to watch and wait for decisive action," he said.
UK Prime Minister Gordon Brown added: "No-one thinks - having seen the results at polling stations - that President Mugabe has won this election.
"A stolen election would not be a democratic election at all," he said. "The credibility of the democratic process depends on there being a legitimate government."
Mr Brown, and other Western officials, are expected to meet Mr Mbeki privately.
The European Union presidency, currently held by Slovenia, has also expressed concern about "the prolonged and unexplained delay in releasing the presidential results which is undermining the credibility of the process".
In Zimbabwe, the MDC's spokesman Nelson Chamisa said the more than 50 arrests were countrywide - relating to minor skirmishes in townships around the capital, Harare and Bulawayo.
South Africa's president is coming under pressure from politicians and protesters to use his influence
One of those arrested is reported to be Chitungwiza MP Marvelous Khumalo.
Zimbabwean police reported arresting 30 MDC supporters for obstruction and intimidation.
Those arrested were found either "barricading roads and stopping people from going to work", "obstructing the free movement of traffic" or intimidating people who went to work, police said.
The MDC's national executive is meeting to decide whether to continue with further strike action. The party had wanted people to stay at home until the presidential election results were released.
But local journalist Brian Hungwe in Harare says most banks, shops and offices opened as usual and armed police and soldiers were on patrol.
MDC Secretary General Tendai Biti told the BBC on Tuesday that two of its activists had been killed and 200 hospitalised after being assaulted by ruling party militias.
Gordon Brown on the Zimbabwean election
The independent Zimbabwe Association of Doctors for Human Rights (ZADHR), in a separate statement, said its members had treated 157 people between the elections and 14 April who had injuries that clearly resulted from organised violence and torture.
"One third of the patients are women, including a 15-year-old girl who was abducted with her mother from her home, made to lie on her front and beaten on her buttocks," they said in a statement quoted by AFP news agency.
"Her mother, who is pregnant, was similarly beaten. Both mother and daughter required hospital admission."
Nine patients had broken bones, mostly in their arms or hands, the statement said, adding that some of the injured would have permanent disabilities.
The election commission says it cannot release the results until a recount in some areas is completed at the weekend.
The situation is more worrying now given the reported violence that has erupted in the country
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.