US Secretary of State Hillary Clinton on Friday held talks with Uganda President Yoweri Museveni and rebels in neighbouring Democratic Republic of Congo attacked government forces in the east, prompting refugees to cross into Uganda, officials said.
"They discussed the problems facing the Congo and the president said that he will ensure that he will find short and long-term solutions to the problem," acting Foreign Minister Henry Okello Oryem told dpa.
After a brief stop in Kampala earlier Friday, Clinton returned to the Ugandan capital from talks in South Sudan.
Congolese militias known as Mai Mai attacked government forces in the village of Lubilia near the Uganda border, sending several hundred refugees into Uganda, a military spokesman said.
Clinton met South Sudan President Salva Kiir hours after the expiry of the UN Security Council's August 2 deadline for South Sudan and Sudan to resolve a border dispute that raised tensions.
Clinton is the most senior US diplomat to visit South Sudan independence from Sudan in 2011 after two decades of civil war..
The failure of negotiators to agree on the demarcation of the border and on sharing revenues from southern oil production by the UN deadline exposes both countries to UN sanctions.
"The problem isn't the South Sudanese but the Sudanese themselves, because it is Khartoum that won't negotiate in good faith," said Nairobi-based International Crisis Group analyst Ernst Hogendoorname.
"The US is arguably the most important partner for South Sudan," he added, indicating the importance of Clinton's visit.
In January, Juba shut down its crude output in protest at taxes levied by Khartoum for the use of Sudan's pipeline, costing the world's newest country 98 per cent of its revenue and sending inflation rates soaring to 80 per cent.
Clinton will on Saturday travel on to Kenya for a joint meeting with President Mwai Kibaki and Prime Minister Raila Odinga in what the State Department described as signalling "support for credible, nonviolent national elections in 2013."
Kenya witnessed weeks of ethnic bloodshed following the disputed presidential vote of December 2007 and a political crisis that required assistance from foreign mediators to broker a power-sharing deal between Kibaki and Odinga.
Next year's election has already courted controversy, as two of presidency challengers to frontrunner Odinga face charges at the International Criminal Court (ICC) in The Hague of orchestrating the 2007-08 violence.
"Washington is a huge donor and strategic ally to Kenya, and its politicians listen to American officials," Hogendoorname told dpa.
"The message is that Kenya needs to focus on preparations for the elections and ensure that those campaigning for the presidency abide by the rules and that hate speech will not be accepted."