At least 220 people are now suspected to have died from the ongoing Ebola outbreak, the head of the World Health Organization said Monday. Dr. Tedros Adhanom Ghebreyesus said that because of a delay in detecting cases, health workers were now "playing catch-up."

The announcement came as Ugandan health authorities reported two new Ebola cases Monday, bringing the number of infections there to seven, after the number of suspected cases in the neighboring Democratic Republic of the Congo surpassed 900.

All the cases are linked to the Congo outbreak, which appears to have started several days or weeks before authorities in that country declared the outbreak on May 15.  

A 59-year-old Congolese man was admitted to a hospital in Kampala, the Ugandan capital, on May 11 and died three days later, before it was known he was suffering from the Ebola virus. Two other Congolese nationals who sought medical care in Uganda later tested positive for Ebola.

Ugandan health authorities on Saturday confirmed the first local infections: a driver and a health worker exposed to the Congolese patient who died on May 11. Two more health workers at a private hospital in Kampala have tested positive, the Ministry of Health said Monday.

In the Congo, suspected Ebola cases have topped 900, mainly in the eastern Ituri province, where the ongoing outbreak is centered, authorities said Sunday, and where confirmed cases are now over 100.

The response has been hampered by fear, anger and frustration among locals including attacks on treatment centers, as well as distrust of authorities in a region long plagued by armed violence.

The World Health Organization has declared the outbreak a public health emergency of international concern.

The Bundibugyo type of Ebola virus responsible for the outbreak has no approved vaccine or treatment, though scientists from the University of Oxford are working on a vaccine that could begin clinical trials in "two to three months," a WHO spokesperson told CBS News partner network BBC News last week.

Gunfire and evacuations

Angry young men stormed a hospital treating Ebola patients in eastern Congo on Sunday evening, forcing the medical staff to scramble to evacuate the patients as gunfire rang out in the area.

It was not immediately known if anyone was hurt in the attack on the Mongbwalu General Hospital but Dr. Richard Lokudu, the hospital's medical director, told The Associated Press the attackers demanded that two bodies of their kin be handed over to them.

There was gunfire and the medics were trying to evacuate the patients and the staff, Lokudu said over the phone.

"Mongbwalu General Hospital is on general alert," he added. He did not have any further details of the unfolding turmoil.

The attack – the third in a week's time on healthcare facilities where medical workers struggle with a lack of resources to treat suspected Ebola cases – underlined the challenges of the outbreak.

Bodies of those who died of Ebola can be highly contagious and lead to further spread when people prepare them for burial and gather for funerals.

In response to the outbreak, Congolese authorities have mandated that the dangerous work of burying suspected victims be managed wherever possible by authorities, which can be met by protests from families and friends. On Friday, the government said funeral wakes and gatherings of more than 50 people would be banned in northeastern Congo in an effort to curb the spread of the virus.

On Saturday, a group of residents of Mongbwalu, located in Ituri province, attacked and set fire to a tent set up for suspected and confirmed Ebola cases by the Doctors Without Borders humanitarian group.

During that attack, 18 people with suspected Ebola infections left the facility and were now unaccounted for, Lokudu had said earlier.

On Thursday, another treatment center, in the town of Rwampara, was burned down after family members were banned from retrieving the body of a local man suspected to have died of Ebola.

WHO has said the outbreak poses a "very high" risk for Congo – up from a previous categorization of "high" – but that the risk of the disease spreading globally remains low.

Earlier on Sunday, the Congolese Ministry of Communication said the total suspected Ebola deaths stood at 119, but the numbers it released separately for each region added up to 220. Officials could not immediately be reached to explain the discrepancy.

The International Federation of Red Cross and Red Crescent Societies said Saturday that three of its volunteers had died from the outbreak in Mongbwalu. The agency said it believed the three healthcare workers contracted the virus on March 27 while handling dead bodies as part of a humanitarian mission unrelated to Ebola.

If confirmed, this would significantly push back the timeline of the outbreak.