Arthur Mutambara, leader of a smaller faction of the opposition Movement for Democratic Change (MDC), was also due to attend the meeting at Mugabe’s State House offices in Harare, he said.
"The principals will be meeting today in an effort to resolve the outstanding issues," a senior official close to the talks told Reuters.
"I don’t think we should be speculating. An agreement will be reached when the outstanding issues have been resolved," he said.
Officials from both Tsvangirai’s main MDC party and Mutambara’s faction declined to comment on the talks.
Talks between Mugabe’s ruling ZANU-PF and the MDC have reached an impasse over who will control key ministries in a unity government to be established under the September 15 power-sharing deal.
A meeting between Mugabe and Tsvangirai on Tuesday failed to lead to a breakthrough, raising fears the deal could break down.