Tanzania is refusing to provide detailed information on suspected Ebola cases, the World Health Organization (WHO) said in a rare public rebuke as the region struggles with an outbreak already declared a global health emergency.

Transparency and speed are key to combating the deadly hemorrhagic fever because it can spread rapidly. Anyone deemed to have been in contact with potentially infected people must be quarantined and the public warned to step up precautions, such as handwashing.

WHO said in a statement late on Saturday that it was made aware on September 10 of the death of a patient in Dar es Salaam, and unofficially told the next day that the person tested positive for Ebola. The woman had died on September 8.

"Identified contacts of the deceased were unofficially reported to be quarantined in various sites in the country," the statement said.

WHO said it was unofficially told that Tanzania had two other possible Ebola cases. One had tested negative and there was no information on the other.

Officially, the Tanzanian government said last weekend it had no confirmed or suspected cases of Ebola. The government did not address the death of the woman directly and did not provide further information.

Despite several requests, "clinical data, results of the investigations, possible contacts and potential laboratory tests performed ... have not been communicated to WHO," the UN agency said.

"The limited available official information from Tanzanian authorities represents a challenge."

Officials in Tanzania's health ministry could not be reached for comment.

Authorities in east and central Africa have been on high alert for possible spillovers of Ebola from the Democratic Republic of Congo, where a year-long outbreak has killed more than 2,000 people.

The WHO was heavily criticized by experts during West Africa's 2014-2016 Ebola epidemic, which claimed more than 11,300 lives in Guinea, Liberia, and Sierra Leone, for not moving more quickly to contain the outbreak, which remains the world's worst.