The World Health Organisation has declared the outbreak of the rare Bundibugyo strain a public health emergency of international concern, and said the risk of a national epidemic in the Democratic Republic of Congo is "very high".
Nearly 750 suspected cases and 177 suspected deaths have been recorded in Uganda's neighbour, the centre of the outbreak.
The WHO has said late detection, the absence of a vaccine or virus-specific therapeutics, widespread armed violence and high mobility among the population make Congo especially vulnerable.
The new cases reported in Uganda on Saturday include a driver who transported the country's first confirmed patient and a health worker exposed while caring for that patient.
Both were receiving treatment and were identified among known contacts, the ministry said in a statement.
The third case is a woman from Congo who entered Uganda with mild abdominal symptoms and later travelled from Arua, close to the border, to Entebbe before seeking care at a private hospital in the capital Kampala.
The patient initially improved and returned to Congo but later tested positive for Ebola after a follow-up prompted by a tip-off from a pilot involved in transporting her.
All identified contacts linked to the confirmed cases are being closely monitored, the ministry said, urging the public to remain vigilant and report suspected symptoms.
