U.S. Secretary of State John Kerry has arrived in the Democratic Republic of Congo, where he will meet with President Joseph Kabila.
The two leaders are expected to discuss recent security gains against rebel groups in eastern Congo.
Kerry commented on Ukraine's unrest shortly after arriving in the D.R.C. capital, Kinshasa, on Saturday. He welcomed the release of international monitors who had been held by pro-Russian separatists in eastern Ukraine for more than a week.
Earlier Saturday, Kerry made a fresh appeal for South Sudan's warring factions to seek peace.
Shortly before wrapping up a visit to Addis Ababa, he pressed for South Sudan's president, Salva Kiir, and rebel chief Riek Machar to engage in direct talks, a move that could end months of deadly violence.
"If both sides do not take bold steps to end the violence, they risk plunging South Sudan into greater desperation and even famine and that famine could be right around the corner if we don't turn the corner ourselves in the next day. They will completely destroy what they claim they are fighting for if we do not make a difference now."
Kerry met with Mr. Kiir in South Sudan on Friday, and later spoke by phone to Machar, in a bid to get the two leaders to attend peace talks in Ethiopia. U.S. officials said Machar did not commit to talks but also did not rule them out.
During his Saturday policy speech in Ethiopia, Kerry also commented on the plight of about 276 Nigerian girls, who remain missing after gunmen kidnapped them from their secondary school last month.
"The kidnapping of hundreds of children by Boko Haram is an unconscionable crime and we will do everything possible to support the Nigerian government to return these young women to their homes."
Kerry also said the U.S. would support Nigerian efforts to bring the perpetrators of the crime to justice. The Boko Haram Islamist militant group has not claimed responsibility for the kidnapping.
While in Addis Ababa, he also met with Somali President Hassan Sheikh Mohamud to discuss Somalia's efforts to fight the al-Qaida-linked militant group al-Shabab.
After a stop in Angola, Kerry returns to Washington Monday.