Zimbabwean opposition leader Nelson Chamisa snubbed an invitation by President Emmerson Mnangagwa to join a national summit on Wednesday, just weeks after security forces crushed protests over the worsening economy."He is not attending," Chamisa's spokesperson Nkululeko Sibanda told AFP ahead of the meeting of political leaders, scheduled to take place at the presidential offices.Chamisa, who insists he won last July's presidential elections, said he was in favour of dialogue but would only attend talks if they were called by a neutral party."The dialogue should be facilitated by someone who is neutral, rather than Mnangagwa being an umpire when his election is in dispute," said Sibanda.Mnangagwa announced via Twitter: "I have invited the leaders of all political parties to come together, without preconditions, to begin a process of national dialogue. "Let us all put the people first and politics second," he said.But Chamisa tweeted that the "presidency is disputed" because of "rigged presidential election result"."We need genuine dialogue under a credible convener and mediator to solve this crisis," he said."Stop citizens' abuses, beatings and arrests," he said. The meeting, due later on Wednesday afternoon, is taking place against a backdrop of worsening economic troubles.The crisis reached breaking point in January when tens of thousands took part in nationwide protests after Mnangagwa more than doubled fuel prices.The demonstrations were brutally crushed, leading to the deaths of at least 12 people, along with documented cases of torture and sexual assault at the hands of the security forces.Hundreds of people including trade union leaders and opposition politicians were detained.Sibanda derided the meeting called by Mnangagwa as a ruse to divert attention from the abuse.Mnangagwa, who took over from long-time ruler Robert Mugabe, has pledged to revive Zimbabwe's sickly economy and end its international isolation.The economy has been in a downward spiral for more than a decade, with cash shortages, high unemployment and recently a scarcity of staples such as bread and cooking oil.Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.