JAKARTA, July 26 (Reuters) - Authorities have found signs of bird flu in chicken droppings near the home of three Indonesians who died from the virus this month, but have not yet linked the discovery to the victims, an official said on Tuesday.

Experts from the Health Ministry have been puzzled by the deaths of a man and his two young daughters near Jakarta due to bird flu, the first human fatalities in the world´s fourth-most populous country.

"Our veterinarian researchers found a positive result from this feces, but whether (the victims) were infected by this is still unknown," said Agriculture Ministry spokesman Hari Priyono.

"Our problem is if it is true that it jumped to humans, the ones who would die first should be the farmers."

The chicken droppings that contained the H5N1, or avian influenza virus, were found near the victims´ family home in Tangerang, a satellite city of Jakarta.

As part of efforts to combat the virus, authorities on Tuesday killed more than 800 chickens at a farm in West Java province, where signs of the bird flu infection were found last week.

Indonesia has prepared 44 hospitals across the country for the treatment of further possible victims.

But in a sprawling archipelago dotted with small farms, and where even many urban families keep chickens, pinpointing the source of the virus is proving difficult.

Avian influenza, which arrived in Asia in late 2003, has so far killed more than 50 people in the region, including Vietnam, Thailand and Cambodia. In Indonesia, the virus has spread to 21 provinces out of 33 over the past two years.

It had already jumped species in Indonesia, having been discovered in pigs on densely populated Java island in May.