Five more people have died from bird flu in Indonesia, the World Health Organization has confirmed.
The bird flu death toll is now 30 in Indonesia
The deaths of the five brings Indonesia's bird flu death toll to 30.
Four of the people who died lived in northern Sumatra and were from the same family. The WHO has sent a team to the area to investigate.
An Indonesian health ministry official told Reuters news agency there was no evidence of human-to-human transmission in the latest cases of the H5N1 virus.
In the cluster of cases in northern Sumatra, up to eight members of a family in Kubu Simbelang village, about 50km (30 miles) south of Medan, could be involved.
Tests are still being carried out to see whether sick relatives also have bird flu.
Scientists are investigating the cause of the outbreak.
"The spread was through risk factors from poultry or other animals. There is no proof of human-to-human," a health ministry official, Nyoman Kandun, told Reuters.
But the agency also quoted an Indonesian agriculture official who said that possibility could still not be ruled out.
"There is a big question mark. Blood samples from all kinds of animals from chickens, ducks, geese, birds, pigs, cats and dogs turned out negative so far. Manure has also been checked. The result is negative," he said.
The outbreak is worrying for officials because it occurred on the island of Sumatra, whereas most cases so far have been recorded in Java.
Worst death rate
The fifth death confirmed on Wednesday occurred in Surabaya in Java. The victim was a 38-year-old caterer whose job involved dealing with livestock and meat. She died last week.
The latest deaths mean 30 people have died from the disease in Indonesia this year - by far the highest death rate in the world in 2006.
Indonesia is second only to Vietnam in the list of countries with most bird flu deaths overall.
However, while Vietnam and third-placed Thailand have managed to slow the spread of the disease and the death toll through tough controls, Indonesia has been criticised for a tardy response.
A senior official at the UN's Food and Agricultural Organization said earlier this week that Indonesia's government had failed to co-ordinate its reaction and raise public awareness.
The H5N1 virus has killed 115 people worldwide since 2003. It has also devastated poultry stocks.
The majority of deaths have occurred in Asia, but cases in people and birds have also been recorded in Europe and Africa.
Almost all human infections so far are thought to have been caused by direct contact with sick poultry.
Experts fear the virus could mutate into a form that passes easily between humans, possibly sparking a pandemic.