Agriculture Minister Gheorghe Flutur said some wild birds had shown they were carrying the virus.
"A swan tested positive with antibodies close to the border with Ukraine, near the village of CA Rosetti," Flutur said on Tuesday.
"A few swans in Maliuc and a wild duck in Ceamurlia de Jos also tested seropositive."
The village of CA Rosetti is 10km from the border with Ukraine, in southeastern Romania.
On Monday, Romania said the bird flu outbreak was limited to Ceamurlia de Jos and Maliuc, 40km to the north.
All 21,000 domestic birds in these two villages have been culled.
On Saturday, British tests identified the H5N1 strain of the disease in three ducks found dead in Ceamurlia de Jos - the first incidence in mainland Europe of H5N1, which has killed more than 60 people and millions of birds in Asia since 2003.
Romania has not reported any cases of bird flu in humans.
Turkey, which also detected the H5N1 strain in birds, tested nine people for possible bird flu last week, but no immediate sign of illness was detected.
Greece on Monday confirmed a case of bird flu on a turkey farm on the Aegean Sea island of Oinouses, near the Turkish coast.
Meanwhile, European Union foreign ministers are holding emergency talks on the widening bird flu scare.
The EU was preparing to ban sales of live birds and poultry from the Aegean Sea region of Chios pending tests on samples taken from turkeys feared infected with the Asian H5N1 strain.
The EU is to ban the sale of live
birds from the Aegean Sea area
Poultry from Turkey and Romania has been banned by the EU as bird flu found there was confirmed as H5N1.
Tests were also being carried out on birds in Bulgaria and Croatia.
Officials said the foreign ministers are to discuss the international response to the westward spread of bird flu and take stock of EU nations' readiness to deal with a possible pandemic.
The H5N1 strain has swept poultry populations in large swathes of Asia since 2003, jumping to humans and killing at least 61 people - more than 40 of them in Vietnam - and resulting in the deaths of tens of millions of birds.
Its spread westward by migrating wild fowl has intensified fears in Europe that the virus could mutate into one that can be easily transmitted among humans - a development that experts fear could provoke a global epidemic that puts millions of lives at risk.
There are concerns of a lack of
vaccines and anti-virals
The EU stepped up biosecurity measures and installed early detection systems along the migratory paths of birds to prevent contamination of domestic flocks.
But there are concerns that European nations lack stockpiles of vaccines and anti-virals to cope with a major outbreak.
Seeking to calm public fears, the head of the EU's new agency for disease prevention on Monday downplayed the risk to humans.
"The risk to human health, to public health, at this stage is minimal," Zsuzsanna Jakab said in Stockholm, Sweden, the EU agency's headquarters.
"The risk to human health, to public health, at this stage is minimal"
Director, European Centre for Disease Prevention and Control
However, she said the European Centre for Disease Prevention and Control was drawing up guidelines on how workers who deal with infected animals can protect themselves against infection.
"There is a little more risk for those who have directly worked with the infected animals, so our goal must be to further minimise that risk," Jakab said.
The World Health Organisation recommends governments keep stocks of anti-viral drugs and regular human flu vaccines to inoculate at least 25% of their populations.
European officials say the 25 nations in the EU, as well as Iceland, Norway and Liechtenstein, have only 10 million doses now for an area of almost 500 million people, and will have only 46 million doses by the end of 2007.
Stockpiling vaccines is difficult as flu viruses can mutate quickly.
On Thursday, EU health ministers open a two-day meeting at a conference centre in Hertfordshire, England, to assess the state of national bird flu preparedness.
There is no human vaccine for the current strain of bird flu but scientists believe the Tamiflu drug may help humans fight bird flu contraction.