BANGKOK (Reuters) - A small group of around 50 rubber farmers gathered in Thailand's southern province of Surat Thani on Tuesday to demand more support from the military-led government for rubber prices, in defiance of martial law.

The law has been in place since May, the same month the military staged a coup to end months of political street protests. The law prohibits all demonstrations and political gatherings of more than five people.

The rubber farmers handed in a petition to Surat Thani Governor Chatpong Chatputi calling for government intervention, the police said. "There are still around 20 farmers gathered around city hall but no violent incidents have been reported," said a police officer in Surat Thani, who declined to be named.

Mr Soontorn Rakrong, a spokesman for 14 farmers' groups based in the south, said farmers had grown increasingly desperate because the government had failed to soften the blow from a collapse in rubber prices.

Weak demand, particularly from top importer China, amid a supply glut has pushed global rubber prices down to five-year lows.

Thailand's benchmark unsmoked rubber sheet (USS3), which farmers sell to factories, was quoted at 43 baht (S$1.70) per kg on Monday.

Farmers are demanding that the government find ways to ensure they get 80 baht per kg, Mr Soontorn told reporters at Government House in Bangkok, where he had gone to seek talks with ministers. "We will give the government until the new year to solve plunging rubber prices. If they can't, farmers from around the country will come to Bangkok to meet Prime Minister Prayuth Chan-ocha," Mr Soontorn said.

The government said on Monday that measures to push the price of USS3 up to 60 baht per kg were already in hand. It has also promised direct handouts to farmers.

A state body is to buy rubber from the market under measures announced in October.

To avoid building up costly stockpiles, the government has said it would only intervene in the market in that way if it had buyers for the rubber it purchased.

On Monday, Deputy Agriculture Minister Amnuay Patisse said China's Hainan Rubber Industry Group had bought 200,000 tonnes, after purchasing 208,000 tonnes in November, but a Chinese source with knowledge of the matter said the second deal had not yet been concluded.