Barack Obama on Monday officially begins a two-day visit to Ethiopia, the first-ever trip by a US president to Africa's second-most populous nation and the seat of the African Union.
Obama, who flew into a rainy Addis Ababa late on Sunday after a landmark trip to Kenya, his father's birthplace, is to hold talks with the Ethiopian government, a key strategic ally but much criticised for its record on democracy and human rights.
He will also hold talks with regional leaders on the civil war in South Sudan in an attempt to build African support for decisive action against the war-torn country's leaders if they reject an ultimatum to end the carnage by mid-August.
On Tuesday Obama will also become the first US president to address the African Union, the 54-member continental bloc, at its gleaming, Chinese-built headquarters.
Air Force One touched down at Addis Ababa's international airport after a short flight north from the Kenyan capital Nairobi, and the president was greeted on the tarmac by Ethiopian Prime Minister Hailemariam Desalegn.
AU Commission chief Nkosazana Dlamini-Zuma has hailed what she said will be a "historic visit" and a "concrete step to broaden and deepen the relationship between the AU and the US".
While Kenya launched one of the biggest security operations ever seen in the capital Nairobi to host Obama from Friday evening to Sunday, the habitual reach of Ethiopia's powerful security forces meant there was little obvious extra fanfare ahead of his arrival.
Ethiopia, like Kenya, has been on the frontline of the fight against the Somali-led, Al-Qaeda-affiliated Shebab. Both nations have troops in Somalia as part of an AU and US-backed force and are key security partners to Washington.
But the visit also comes two months after elections that saw the prime minister's ruling coalition take every one of the 546 seats in Ethiopia's parliament. The opposition, which lost its only seat, alleged the government used authoritarian tactics to guarantee victory.
The US State Department has noted Ethiopia's "restrictions on freedom of expression," as well as "politically motivated trials" and the "harassment and intimidation of opposition members and journalists".
Tough on South Sudan
Ahead of the visit, the White House stressed it frequently addresses issues of democracy and political rights in the region. Having spoken frankly in Kenya on human rights and corruption, Obama is now expected to address Ethiopia's -- and Africa's -- democracy deficit.
But Ethiopia has come far from the global headlines generated by the 1984 famine, experiencing near-double-digit economic growth and huge infrastructure investment that have made it one of Africa's top-performing economies and a magnet for foreign investment.
Through the tinted windows of his bomb-proof presidential limousine, nicknamed "The Beast," Obama will see Addis Ababa's construction boom of tower blocks, as well as sub-Saharan Africa's first modern tramway.
High on the agenda Monday are talks with leaders from Ethiopia, Kenya and Uganda as well as Sudanese Foreign Minister Ibrahim Ghandour to try and build a collective front to end the 19-month civil war in South Sudan, the world's youngest nation.
Signalling a deeper commitment to ending violence that has killed tens of thousands of people and forced more than two million from their homes, Obama is expected to make the case for tougher sanctions and a possible arms embargo.
South Sudan's warring leaders -- President Salva Kiir and rebel leader Riek Machar, who will not be at the meeting -- effectively face an ultimatum, a "final best offer," according to one senior administration official.
"The parties have shown themselves to be utterly indifferent to their country and their people, and that is a hard thing to rectify," the official said.
South Sudan, midwifed into existence by US cash and support in 2011, has faltered badly in its infancy and the Obama administration has been accused of abandoning the fragile nation.
"America bears a unique responsibility to end the war in South Sudan given its role in the creation of the country," said Casie Copeland, an analyst for the non-profit International Crisis Group.
"The failure to more seriously try and bring about peace is an abdication of its moral responsibility."