ADDIS ABABA - Ethiopia's new leader Hailemariam Desalegn, expected to assume power following the death of the country's longtime prime minister, readied for the post Friday after holding talks with US President Barack Obama.

But Hailemariam, 47, a relatively little known politician overshadowed by his mentor Meles Zenawi, who died on Monday, faces tough challenges both internally and across the wider volatile Horn of Africa region.

Obama, who telephoned Hailemariam late Thursday, urged him to "use his leadership to enhance the Ethiopian government's support for development, democracy, human rights and regional security," the White House said.

Hailemariam has also met with South Sudan's foreign minister and his Kenyan counterpart, who were in Addis Ababa on Thursday to pay their respects to Meles, who died aged 57 after a long illness.

Official mourning continues for Meles, with crowds gathering for a third day in the grounds of the National Palace, where photos of the late leader are on display.

Scores of police and army officers alongside ordinary citizens, many weeping loudly, have gathered to pay their respects ever since his body was flown home following his death in a Brussels hospital.

But the political process continues behind doors. Government spokesman Bereket Simon has said Hailemariam is expected to be formally sworn in in a emergency parliament session at "any time."

In a rare peaceful handover of power in Ethiopian history, former water engineer Hailemariam took over as interim leader on the death of Meles, who had ruled with an iron-fist since toppling dictator Mengistu Haile Mariam in 1991.

A close ally of Meles as deputy prime minister and foreign minister since 2010, Hailemariam was elected deputy chair of the ruling coalition Ethiopian Peoples' Revolutionary Democratic Front (EPRDF) after the party's fourth win, a landslide victory in 2010.

In a country long dominated by the major ethnic groups -- most recently the Tigray people, like Meles -- Hailemariam notably comes from the minority Wolayta people, from the Southern Nations, Nationalities and Peoples Region.

He served as president for the region -- the most populous of Ethiopia's nine ethnic regions -- for five years.

But within the coalition, some of the most influential figures hail from the northern Tigray region, members of Meles's ex-rebel turned political party, the Tigrayan People's Liberation Front (TPLF).

-- 'Seen as a figurehead --

Analysts have suggested that several others are still jostling for power behind doors in the often secretive leadership, even if in the open they may not take part in the running for the top job.

"Many see him as a figurehead, part of a gesture by Meles and the ethnic Tigrayans to give more prominence to other ethnic groups," said Jason Mosley of Britain's Chatham House think-tank.

He is also a Protestant, unlike the majority of Ethiopia's Christians, who follow Orthodox traditions.

But others less critical warn that while outside the Tigray power base, that could in fact be a strength.

"His ethnicity is considered an advantage, because it is a minority in a multi-ethnic region and, most importantly, not from the numerically dominant Oromo or Amhara," the International Crisis Group said in a recent report.

Critics also point to his relatively young age, lack of experience and the fact he was not part of the rebel movement which toppled Mengistu, unlike many in the ruling elite.

Instead, Hailemariam, who studied civil engineering in Addis Ababa, was completing his masters degree at Finland's Tampere University when Mengistu fell.

Hailemariam, while a protege of Meles, is therefore seen as an outsider by some.

"He is a political novice, he has not been part of the old guard, he has not been in the bushes fighting with the rebels," Berhanu Nega, an exiled opposition leader and former mayor of Addis Ababa, told the BBC.

"He is a Medvedev for a group of Putins in the ruling party with their own internal squabbles," he added, drawing parallels with Russian political dynamics.

The government however has insisted Hailemariam will remain in the post until elections due in 2015, although he must first be formally chosen as head of the ruling EPRDF party, likely later this year.

"The secession issue has been settled for good," said spokesman Bereket.