Talks between Zimbabwe's political parties on the formation of a power sharing government got underway in earnest on Thursday in South Africa.

Negotiators from President Robert Mugabe's Zanu-PF party, opposition leader Morgan Tsvangirai's Movement for Democratic Change (MDC) and a splinter MDC faction led by Arthur Mutambara had begun the talks at a secret location, a senior MDC source said.

The negotiators chosen to represent each faction are the same as during the initial "talks about talks" that took place last week in Pretoria, with the addition of MDC Women's Assembly chairperson Theresa Makone and chairperson Lovemore Moyo as observers.

Tendai Biti, secretary-general of Tsvangirai's MDC faction is the biggest name on the opposition side, while Mugabe is represented by reappointed justice minister Patrick Chinamasa and labour minister Nicholas Goche, the MDC source said.

On Monday, Mugabe, Tsvangirai and Mutambara signed a memorandum of understanding setting out the agenda and the ground rules for the talks on the formation of an "inclusive" government. Among other things, all parties have been ordered to respect a media blackout on the talks.

Analysts have said that it will likely take more than two weeks, given the high level of distrust between the parties, for them to reach agreement on divisive issues, such as who should lead the next government.

Mugabe claims he is the country's rightful leader after he was sworn in for a further five years as president in June following an election run-off he alone contested.

The MDC and Western powers such as Britain say Tsvangirai should have the most powerful role, because he won the first round of the presidential elections in March. Tsvangirai boycotted the late-June run-off after youth militia loyal to Mugabe killed dozens of his supporters.

Mugabe, 84, has governed Zimbabwe since independence in 1980. His increasingly authoritarian rule and populist policies have been blamed for the country's economic collapse, as characterised by official inflation of 2.2 million per cent and widespread food and fuel shortages.

The European Union on Tuesday tightened sanctions against Mugabe's regime, slapping a further 36 of his political and military aides with travel bans and blacklisting four companies linked to his government.