Pakistan's health ministry said Monday it was still investigating whether there was human transmission in the country's first death from bird flu.
It said initials tests by the World Health Organisation (WHO), which sent a team here last week, had ruled it out but that Pakistan had sent samples to Geneva -- the WHO's headquarters -- for further confirmation.
Scientists fear that if the virus were passed from one person to another, rather than from infected birds, it might indicate a mutation that could lead to a global pandemic with the potential to kill millions.
"In their preliminary tests the WHO team excluded suspected human-to-human transmission, but we have sent the samples to Geneva for further confirmation," health ministry spokesman Oriya Maqbool Jan told AFP.
The WHO team was sent after the ministry announced the death of a man who was one of six people infected with the deadly H5N1 strain of the avian influenza virus in North West Frontier Province along the Afghanistan border.
A brother of the victim also died before being tested for the virus. Both had worked on a cull of infected poultry.
"We have been very closely monitoring the situation," said Rafiqal Hasan Usmani, the animal husbandry commissioner. "There has been no new outbreak."
The H5N1 strain of bird flu has killed more than 200 people worldwide, mostly in Southeast Asia, since late 2003.