BANGKOK (AFP) - A media rights group Thursday called for the dismissal of "baseless" charges against three people accused of spreading false rumours about the Thai king's health that sent stocks plunging last month.

Reporters Without Borders (RSF) said the three Thai Internet users arrested this month were being used as "scapegoats" for October's drop in the market over concerns about the condition of revered King Bhumibol Adulyadej.

"We call for the charges against these three Internet users to be dismissed," said the RSF statement.

"Such accusations are baseless and violate the right to report an economic event after it has taken place. Explaining that the stock exchange fall was linked to the king's health harms neither the king nor national security."

The 81-year-old monarch, regarded as a demi-god by many Thais and as a stabilising force in a politically turbulent nation, has been in hospital since mid-September with a lung infection and fever.

On Sunday police arrested Katha Pajariyapong, of brokerage company KT ZMICO, and Theeranan Vipuchanin, a former executive with UBS Securities, for allegedly damaging national security by posting false information on the Internet.

Somjet Sitthiworakul was then arrested Tuesday on the same charge, under a computer crimes act. If convicted they could face up to five years in jail or a 100,000 baht (3,000 dollar) fine.

The Thai bourse plunged 8.22 percent at one point on October 15 over the rumours.

RSF said the defendants had only posted articles online that linked the fall in stocks to the fact that the king was admitted to Bangkok?s Siriraj Hospital on 19 September.

The media group said Theeranan pointed out that she had only translated and posted a Bloomberg News agency article written after the fall and that she was not paid to do so.

"It seems that the translation of the Bloomberg dispatch is the only piece of hard evidence in the prosecution case file," said RSF.

"The investigators have not mentioned the original article and have referred only to the translation, which reinforces the impression that the three defendants are being used as scapegoats for the fall in stocks."

Thailand also has a strict lese majeste law under which insulting or defaming any members of the royal family is punishable by up to 15 years in jail.