Automatic gunfire crackled in the streets of Harare Wednesday as soldiers stepped in to disperse protesters who had clashed with police after the main opposition leader accused the ruling party of trying to rig the result of Zimbabwe's election.
European Union observers also questioned the conduct of the presidential and parliamentary poll, Zimbabwe's first since Robert Mugabe was forced to resign following a de facto coup in November after nearly 40 years in power.
The observers expressed concern about delays in releasing the results of the presidential contest.
The leader of the opposition Movement for Democratic Change, Nelson Chamisa, said on Twitter he had won the "popular vote" in Monday's election, in which he challenged Mugabe's successor, Emmerson Mnangagwa from the ruling Zanu-PF party.
Mnangagwa also took to Twitter, calling for calm and urging patience before the results were announced.
Opposition supporters burned tires in the center of the capital Harare, blocking some streets and engaging in running battles with police who fired water cannon to disperse the protesters.
Soldiers then arrived at the scene, jumping out of several armored personnel carriers. Gunfire was heard and an army helicopter flew in the skies above Harare, witnesses told Reuters.
The electoral commission had said it would start announcing results for the presidential race from Tuesday morning but this was delayed as commissioners read out more parliamentary results.
With three seats yet to be declared, ZANU-PF had 144 seats compared to 61 for the MDC, meaning the ruling party achieved a two-thirds majority which would allow it to change the constitution at will.
Opposition leader Chamisa accused the ZANU-PF of trying to steal the election. He accused the commission of releasing the parliamentary results first to prepare Zimbabweans for a Mnangagwa victory.
The EU's Chief Observer, Elmar Brok, said he did not yet know if the shortcomings would have a material effect on its outcome, and he criticized the Zimbabwe Electoral Commission (ZEC) for being at times "one-sided".
Zimbabwe was once one of Africa's most promising economies but under Mugabe's rule became tainted by corruption, mismanagement and diplomatic isolation. Its population of 13 million is struggling amid shortages of foreign currency, unemployment above 80 percent and lack of foreign investment.