"The Sultanpur Sanctuary was closed on January 10 after the department found 45 birds dead. However, it is too early to comment whether the birds died due to avian influenza virus (H5N1)," District Forest Officer Kulwinder Singh said.
He, however, said no more dead birds have been found in the sanctuary or nearby areas in the last two days.
The carcasses of the birds have been sent to the National Institute of High Security Animal Diseases in Bhopal for avian flu tests, Singh said, adding that the report will come after 10 days.
However, sources in the sanctuary claimed that the birds died as they had eaten pesticide-infested crops at a nearby field.
Of the 45 dead birds, 35 are Eurasian coots, eight are common moorhen, one spot-billed duck and one jungle babbler.
The Sultanpur National Park is located on Gurgaon-Jhajjar Road.