"We suspect an outbreak of bird flu judging by the number of people who have fallen ill with bird flu symptoms," North Sumatra provincial health office chief Chandra Syafei told AFP.
"We are now waiting for the results of blood samples we sent to Jakarta."
The official could not confirm that three people had died from bird flu-like symptoms after the suspected outbreak hit Air Batu village last week.
A nurse at a local hospital that was treating some of the 13 people feared to have contracted the deadly virus told AFP on Wednesday that three people had already died.
Residents of the village became ill with fevers and respiratory problems after a large number of chickens died suddenly with what appeared to be symptoms of avian influenza, officials said.
Syafei said a team of five epidemiologists had been sent to the stricken area to investigate the possible outbreak and distribute antiviral flu medicine Tamiflu.
"They are working together with local officials and the local husbandry office to prevent any eventuality," he said, adding however that the area had not been quarantined.
Health ministry officials in Jakarta have not been available not comment on the suspected outbreak.
The ministry announced earlier this week that the human toll from avian influenza in Indonesia had risen to 112 with the recent death of a 19-year-old man from Java island.
The deadly H5N1 strain of bird flu has killed more than 240 people worldwide since late 2003.
Indonesia is the country worst-hit by the virus, which typically spreads from bird to human through direct contact.
Experts fear it could mutate into a form easily transmissible between humans and kill millions in a global pandemic.