By Madeline Chambers

BERLIN, Oct 2 (Reuters) - German Chancellor Angela Merkel visits three African countries this week and will press South Africa's Thabo Mbeki to take a tougher line with Zimbabwe, in the grip of an economic crisis critics blame on the government.

Merkel will stop in Ethiopia and Liberia as well as South Africa on her first trip to sub-Saharan Africa as chancellor.

"Zimbabwe will be an important subject. Developments there are still massively problematic," a senior German government official told reporters before the visit, starting on Thursday.

Critics accuse President Robert Mugabe of human rights abuses and of presiding over the collapse of Zimbabwe's economy, which has the world's highest inflation rate of about 6,000 percent and unemployment levels of about 80 percent.

"The chancellor will talk about this with Mbeki and urge him to exercise his influence on Zimbabwe to change the developments of the last few years," the official said.

Some Western states have been frustrated by Mbeki's "quiet diplomacy" towards his neighbour which they see as too soft.

The official said Merkel had no intention of following British Prime Minister Gordon Brown's example and threatening to stay away from an EU-African summit in Lisbon in December if Mugabe attends.

"The chancellor will take part in the summit," said the official. "EU-Africa relations should not be held hostage to developments in Zimbabwe. It is in our interests to go through with the summit."

Last month, Brown said it would be inappropriate for him to go, as Mugabe would distract from the main agenda and urged other countries to raise pressure on Zimbabwe. However, many African leaders want Mugabe there to help tackle the continent's problems.

Mugabe, 83, is subject to an EU travel ban but it could be suspended to allow him to attend the summit.

In power since independence from Britain in 1980, Mugabe says the West has sabotaged the economy as punishment for his seizure of white-owned farms and their transfer to landless blacks.

Merkel put tackling poverty in Africa on the agenda of the Group of Eight industrialised countries during her presidency of the grouping this year.

Merkel will meet Ethiopian Prime Minister Meles Zenawi and African Union Commission Chairman Alpha Oumar Konare on Thursday, and Mbeki and his predecessor Nelson Mandela in South Africa on Friday and Saturday.

To round off her five-day trip, Merkel will be in Liberia on Sunday to meet President Ellen Johnson-Sirleaf and discuss the prospects of post-conflict countries and good governance.

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