Mugabe assumed the largely ceremonial role on Friday at an African Union (AU) summit in Addis Ababa as it leaders and UN chief Ban Ki-moon called for global action against Boko Haram in Nigeria.

AU leaders plan to deploy a 7,500-strong multinational force to fight the radical Islamist militia blamed for mass killings in Nigeria's northeast in recent years.

For its force, the AU is expected to ask for UN Security Council approval, plus a "Trust Fund" to pay for it, AU commission head Nkosazana Dlamini-Zuma told the summit.

As new chairman, Mugabe, 90, replaces Mauritania's President Mohamed Ould Abdel Aziz.

"I humbly accept your collective decision, " Mugabe told the summit leaders who elected him as he accepted the post.

Controversial figure

Western nations accuse Mugabe, a former guerrilla leader who fought against white-minority rule in former British-ruled Rhodesia, of crushing political dissent and ruining Zimbabwe's rural-based economy.

For many in Africa, however, he became an anti-colonial hero. Since independence in 1980, his ZANU-PF party has won every election.

Last year, Mugabe boycotted an EU-Africa summit in Brussels after he was given a rare invitation, but his wife was denied a visa.

Harare-based political analyst Earnest Mudzengi said Mugabe as new AU chairman was unlikely to bring about answers to problems across Africa.

"Problems affecting the continent are complex and Mugabe will only be exposed to them and no changes are expected," Mudzengi said.

One African diplomat told the news agency AFP: "It's not a very encouraging sign. The Mugabe style belongs to a past generation, the one that takes power hostage, and this is no longer the AU creed."

Ebola and elections

Summit leaders gathered in Ethiopia's capital will also discuss the economic recovery of countries affected by the Ebola virus, the setting up of a "solidarity fund" and planning a proposed African Centre for Disease Control.

The summit will also focus on more than a dozen elections which are due to take place this year across Africa.

Addressing the conference, the UN's Ban told African leaders that they "cannot afford" to ignore the wishes of their citizens.

"People around the world have expressed their concern about leaders who refuse to leave office when their terms end. I share those concerns."

"Undemocratic constitutional changes and legal loopholes should never be used to cling to power," Ban said.

ipj/gb(AFP, Reuters, AP)