The new scare comes amid accusations that the government is mishandling the crisis in the country's remote east.
With the disease now at Europe's doorstep, experts from the World Health Organisation (WHO) arrived in Turkey, but bad weather forced them to postpone a trip to the infected areas.
Health Minister Recep Akdag said avian influenza had been detected in a fourth person, currently under treatment in a hospital in the city of Van, after officials confirmed three human cases on Friday.
The minister did not specify whether the virus was the lethal H5N1 strain blamed for the death of two siblings in the same hospital over the past week, the first human fatalities from bird flu outside South-east Asia and China.
"There are four cases confirmed by the labs, two are dead- as you know- and the other two are still living," Mr Akdag told the public TRT television.
Results from a third sibling who also died were negative.
The three children perished after playing with the head of a slaughtered chicken which the impoverished family ate after it fell sick.
They came from Dogubeyazit, near the border with Iran, the town where most of some 30 patients undergoing treatment lived.
As worried people rushed to hospitals across the country and the emergency culling of fowl continued, Mr Akdag ruled out human-to-human transmission, a possibility that could spark a global pandemic.
Humans are currrently thought to contract bird flu only through close
contact with infected birds.
But scientists fear that millions could die if the virus crosses with human flu strains to become highly contagious.
Avian influenza (bird flu) has also been reported in three more regions across Turkey.
Dead chicken tested positive in a village in the north-western province of Bursa, some 1,400 kilometers from the worst-hit areas in the east.
The province is the most western point in the country where the virus has been detected.
Earlier, Agriculture Minister Mehdi Eker said samples from wild pigeons in the eastern provinces of Erzincan and Bitlis also tested positive, without specifying whether it was the H5N1 strain.
Bird flu has also been confirmed in wild ducks in an area close to Ankara.