Twenty-two people were injured Friday after violent overnight clash between riot police and rubber farmer protesters in Thailand's southern rubber-producing provinces.

The clash took place at a protest site on Phetkasem road in southern Prachuap Khiri Khan province after a group of rubber farmers hurled rocks and bottles filled with chemical substances to the police, and the police had to use tear gas to disperse the protesters.

Twenty-two people were injured in the clash, most of whom were policemen and 12 protest leaders were detained for questioning.

Deputy Prime Minister Pracha Prommok said he was assigned by Prime Minister Yingluck Shinawatra to negotiate with the rubber farmers to end the protest, adding that he did not expect the confrontation could end immediately.

However, he believed a proposal that could satisfy the rubber planters and be accepted by the government could be the best solution to the problem.

Friday is the eleventh day of street protest by rubber growers against falling rubber prices in the southern rubber-producing provinces, including Nakhon Si Thammarat, Surat Thani, Chumphon, Phatthalung, Trang and Prachuap Kiri Khan.

The protesters demand that the government guarantee the price at 100-120 baht (3.0-3.7 US dollars) per kilogram and rejected the government's fertilizer subsidy offer, claiming that rubber growers would not benefit from the measure. The government, however, stood firm that they would not intervene in the setting of the price.

The government decided Thursday to set up a tripartite committee to work out assistance for rubber farmers as the Natural Rubber Policy Committee (NRPC) stood firm against guaranteeing rubber price as demanded by protesters.

In a related development, railway service between Bangkok and Thailand's South resumed Thursday night after rubber growers called off their blockade in Nakhon Si Thammarat's Cha-uat district.

Iad Seng-iad, a protest leader in the province, said the railroad and the road in Cha-uat district, Nakhon Si Thammarat, were reopened after 10 days of blockade.

He said his group would temporarily suspend their protest for a week to wait for the government's response following a slump in rubber price. They may relaunch the blockades if the government does not come up with satisfactory measures.