Mugabe's Reign of Terror looks to be lengthened
MDC leader Morgan Tsvangirai is said to be under pressure to pull out in view of escalating poll-related violence.
The MDC says dozens of its supporters have been killed but President Robert Mugabe blames the MDC for the violence.
A withdrawal threat could be a move to pressure the international community to ensure a fair vote, say correspondents.
A meeting of senior MDC officials in Harare has revealed "differences of opinion" within the party over its next move, MDC spokesman Nelson Chamisa states.
He said the party needed to assess the situation in the country and unless conditions changed the vote would be a "charade".
If they do pull out, the MDC would be handing victory to President Robert Mugabe, making it a tricky decision to take, says the BBC's Caroline Hawley in Johannesburg, South Africa.
However, Mr Tsvangirai's potential withdrawal from the election can be seen as a move to put pressure on the international community to do something about the poll-related violence in Zimbabwe, says our correspondent.
Economic freefall
Meanwhile in Brussels, the EU has drafted a summit statement saying they are ready "to take additional measures against those responsible for violence".
The EU document does not state what the additional measures might be.
The EU already has an arms embargo against Zimbabwe and has placed travel bans and frozen the assets of President Mugabe and other senior government and ruling Zanu-PF party officials.
Mr Mugabe blames the sanctions for causing Zimbabwe's economic freefall.
The EU statement urged the African Union and the Southern African Development Community (SADC) to deploy "a significant number of election monitors as soon as possible and to ensure their continued presence until the electoral process is completed".
Treason charge
Morgan Tsvangirai gained the most votes in the election's first round, but not enough to win outright.
The opposition has suffered five violent deaths in recent days, among them the wife of Harare's mayor-elect.
The MDC says at least 70 of its supporters have now been killed and 25,000 forced from their homes in a state-sponsored campaign of violence.
 Robert Mugabe Zanu-PF blames the opposition for the violence |
One of its top leaders, Tendai Biti, has also been charged with treason and subversion.
A Harare court has upheld the charges, saying there is reasonable suspicion that Mr Biti committed an offence, and remanded the case to 7 July.
The subversion charge carries a possible death sentence.
MDC rallies have also been disrupted and Mr Tsvangirai briefly detained by police on several occasions.
There has been growing international condemnation, including from some of Zimbabwe's neighbours, of the pre-election climate in the country.
Three countries from SADC monitoring the polls - Tanzania, Angola and Swaziland - said the election would not be free and fair given the current circumstances.
"The report we received still indicates that violence is escalating throughout Zimbabwe," Tanzanian Foreign Minister Bernard Membe told the BBC.
US Secretary of State Condoleezza Rice said violence from Zanu-PF supporters meant the run-off would not be free and fair.
