DHAKA, March 28 (Reuters) - Bangladesh has called for international help to upgrade bird flu testing, an official said on Wednesday, as the country battles a large outbreak of the disease in poultry.

"We have invited donor representatives to a meeting today to discuss the situation and formally ask their assistance," C.S. Karim, head of the fisheries and livestock ministry, said on Wednesday.

Samples are sent to the Bangladesh Livestock Research Institute but the laboratory cannot do the full range of testing needed to confirm the presence of the H5N1 bird flu virus.

Samples have to be sent to Bangkok for confirmation, a costly and time-consuming step.

"If we had the appropriate technology we could confirm the outbreak of the virus at least two-weeks earlier," a veterinary expert said, asking not to be identified.

About 55,000 chickens have been culled since the outbreak of avian flu was confirmed in nine farms near the capital Dhaka and northern Jamalpur district last week. No humans have been confirmed infected.

A U.N. official said they suspected bird flu had been raging in the country for several weeks or months before authorities could confirm it.

Bangladesh needed equipment and training for the staff at the laboratory, another official of the fisheries and livestock ministry said.

The government reiterated on Wednesday that no humans had been infected by H5N1 so far in Bangladesh. But about 100 workers from the nine infected farms remain under close surveillance.