Rwanda on Tuesday accused Uganda of supporting rebel groups opposed to President Paul Kagame's government, amid a resurgence of hostility between the African neighbors.
Relations between the two nations soured last week after Rwanda blocked Ugandan cargo trucks from entering its territory at the busiest crossing point, Katuna, and barred its nationals from crossing into Uganda.
Officials in Kigali say they have directed trucks to another border point 100 km (60 miles) away, but hundreds of them are still stuck at the frontier.
Rwandan Foreign Minister Richard Sezibera accused Uganda of offering succor to two foreign-based Rwanda rebel groups — Rwanda National Congress (RNC) and Democratic Forces for the Liberation of Rwanda (FDLR).
"RNC and FDLR work from Uganda with support of some authorities there. This is another serious case and we have raised it with them," he told a news conference in Kigali.
The RNC is a rebel group led by some of Rwanda's most prominent dissidents including South Africa-based Kayumba Nyamwasa. Its founders say it is a political party.
The FDLR is a rebel group composed in part of former Rwandan soldiers and Hutu militias who fled into Democratic Republic of Congo after massacring around 800,000 Tutsis and moderate Hutus during Rwanda's 1994 genocide.
The group has since sought to topple Kagame's government.
Ugandan Foreign Minister Sam Kutesa said the accusations were false. Uganda could not allow anyone threatening a neighbor "to operate from its territory," he said.
Rwanda and Uganda have a shared political, ethnic and security history that has alternately been friendly and hostile over the decades.
Kagame fought in a guerrilla war that brought Uganda's Yoweri Museveni to power in 1986. Years later, Uganda backed Kagame's rebel group that helped end the Rwandan genocide and took power in Kigali.
Sezibera also accused Uganda of incarcerating, torturing and illegally deporting its citizens "for reasons we don't understand." Rwanda had recorded 190 such cases, he said.
"When some people are deported they reach our border in poor health. This has been happening for a long time and there is no solution so far," he said.
More than a hundred cargo trucks carrying fuel, food, construction materials and other items from Kenya and Uganda have been stranded at Katuna, the busiest crossing point on the Rwanda-Uganda border since the blockade started on Feb. 27.
Rwanda depends for much of its imports on a trade route through Uganda to Kenya's Indian Ocean port of Mombasa. The same artery is also a pipeline for goods from Kenya and Uganda to Burundi and parts of eastern Democratic Republic of Congo.