While insisting that outbreaks of the H5N1 virus are so far restricted to only two areas - Phichit's Bang Moon Nak district and Nakhon Phanom' s Na Klang sub-district - Charal Trinwutthipong, vice agriculture minister, said authorities still had to beef up surveillance programmes to prevent the virus spreading.

The livestock chiefs of the 21 provinces listed as high risk were called to the emergency session at the ministry in Bangkok today.

Charal said some provinces might have to increase surveillance. Fear of further outbreaks came after the Department of Livestock Development (DLD) found the H5N1 virus in commercial chicken farms in Nakhon Phanom and culled 300,000 fowl last weekend.

Chaweewan Leaw-wichak, the DLD's deputy director-general, said during a trip to Nakhon Phanom that the problem after the mass culling was finding a suitable place to bury the chicken carcasses.

Many potential sites were flooded by rainwater. Livestock officials had to spend time pumping the water out and the burial process was moving slowly, she said.

As well as Nakhon Phanom and Phichit, 14 other provinces had reported chickens dying in suspicious circumstances.

Officials in those provinces were waiting for laboratory testing by the DLD to identify the cause of death in the fowls, according to the DLD's website.

The latest area to report dead chickens was Nakhon Sawan's Chum Saeng district, which adjoins already infected Phichit.

The number of suspected human cases of avian flu has increased from 45 to 51 in 17 provinces, including one in Bangkok.

Of the 765 people who were being closely monitored by the Public Health Ministry after the slaughter in Nakhon Phanom, all were in good health, said Dr Pratch Boonyawongwiroj, permanent secretary of the ministry.

Two of six people who had developed high fever were confirmed by laboratory test as being free from H5N1. They were discharged yesterday, while the other four were still waiting for test results.

Meanwhile, the Government Pharmaceutical Organisation (GPO) has made progress in the production of its own version of oseltamivir, the anti-viral drug for influenza that can be used to treat bird-flu patients.

Dr Mongkol Jiwasantikarn, the GPO's director, said the drug was being tested for bio-equivalency by Siriraj Hospital. The results would determine whether the GPO's version of oseltamivir was of the same quality as the original.

Mongkol said if the drug passed the test, the GPO would be able to begin production by November, at a capacity of 400,000 capsules per day. However, he said the raw materials currently available to the GPO were sufficient to produce only one million capsules.

The GPO's version of oseltamivir, once it reached the market, would cost only Bt70 per capsule, much cheaper than the original, which cost Bt120, Mongkol said.