Ugandan citizens returning to the country with a history of travel to Democratic Republic of Congo will be quarantined for 21 days, Health Minister Chris Baryomunsi said on Sunday as Uganda tightened Ebola precautions.

Uganda says it is Ebola-free after declaring an end to its latest outbreak in July, but there has been concern among health experts after two people who had recently passed through the country later tested positive in Kenya and Nigeria.    

Uganda says it is investigating the Nigerian case, which involves the wife of a Swiss diplomat. The woman, 42, returned from Uganda through Addis Ababa to Abuja on October 3, according to Nigeria's Centre for Disease Control, which said she is in isolation and has improved remarkably.

The agency said 53 contacts had been traced.

Ugandan officials are reviewing genomic sequencing, travel information, interactions and movements in coordination with Nigerian authorities and international partners.

Swiss authorities had said the woman is believed to have contracted the virus in Uganda. Baryomunsi pushed back, saying Switzerland was "speaking prematurely". He said the woman's relatives from West Nile visited her in Kansanga, a suburb of Kampala, and that those relatives had visited Congo.

"What evidence do they have that she never travelled there?" he said. "We should speak science, not politics."

Kenya's first Ebola patient had travelled from Congo to Uganda and taken a flight from Entebbe airport to Nairobi on October 3. The patient died two days later.

Both the Kenyan and the Nigerian cases travelled through the same Ugandan airport on the same day but there was no physical interaction between the two, Diana Atwine, the health ministry's permanent secretary, told the press conference, citing a review of the airport's CCTV system.

Baryomunsi said all 60 contacts linked to a Kenyan Ebola case had completed their 21-day monitoring period and been discharged.

"The ministry has intensified traveller screening at Entebbe International Airport and all land border crossings. All travellers intending to enter Uganda by air, land or water must complete the passenger locator form," he said.

Genomic analysis of Nigeria's only confirmed Ebola case showed the virus was closely related to the strain detected in Kenya's index case, though Nigerian authorities said there was no evidence that the Kenya case travelled to Nigeria or had a direct connection.

Uganda borders Congo, where the outbreak began, and has previously battled Ebola outbreaks.

Late on Sunday, World Health Organization Director-General Tedros Adhanom Ghebreyesus said a nurse was killed and a health worker severely injured when they were attacked while responding to an Ebola alert in the northern Congolese town of Bafwasende.

"Everyone working to protect communities from this deadly disease must be able to work in dignity and safety," he wrote on X, saying the attack occurred on Saturday.