"He is not going. He was denied a passport," Movement for Democratic Change spokesman Nelson Chamisa told Reuters.
The meeting of the heads of state of Angola, Swaziland and Mozambique — who form the security committee of the Southern African Development Community — is aimed at trying to help Zimbabwe’s political rivals break a deadlock in negotiations on forming a cabinet.
Four days of talks mediated by former South African president Thabo Mbeki last week failed to end the impasse over the allocation of ministries in a new unity government.
The MDC’s Chamisa said Tsvangirai was given an emergency travel document on Sunday valid only for Swaziland and not for South Africa which he needs to pass through.
"There is no way you can expect him to be in Swaziland when they are making it difficult for him," Chamisa said.
Zimbabwean Information Minister Sikhanyiso Ndlovu dismissed the MDC claim as "a gimmick".
"That’s not true. He has been given a travel document. South Africa is mediating, how can they deny him passage?"
There were signs of failure before the summit opened.
The MDC said on Monday events in the past 24 hours had made it extremely difficult to believe in the mediation process to end the deadlock on forming a cabinet.
"There have been developments in the past 24 hours that make it incredibly difficult for the MDC to have confidence in the current mediation process. Their faith and hope in the current mediation process and its ability to deliver a solution to the people of Zimbabwe is now called into question," the MDC said in a statement.
Tsvangirai said on Sunday that he believed the parties would finalise a power-sharing deal at the meeting.
A September 15 power-sharing agreement, brokered by Mbeki, may be Zimbabwe’s best hope for rescuing an economy where fuel and food are scarce and inflation stands at 231 million percent.
President Kgalema Motlanthe of economic powerhouse South Africa, the current chair of SADC, will lead a delegation to the meeting, according to the Foreign Ministry.
In remarks published in a state-run newspaper on Sunday, ZANU-PF’s chief negotiator, Patrick Chinamasa, played down the issue of cabinet post allocations.
He insisted that Zimbabwe’s ruling party would not bow to any pressure from SADC, which has become increasingly frustrated by Zimbabwe’s political turmoil.
Tsvangirai beat Mugabe in a presidential election on March 29 but with too few votes to avoid a June run-off, which was won by Mugabe unopposed after Tsvangirai pulled out, saying his supporters had been subjected to violence and intimidation.