(Adds comments from Thai premier, recasts)
BANGKOK, Oct 29 (Reuters) - Police may charge four or five people suspected of spreading rumours about the health of the country's 81-year-old king that triggered a slide in Thailand's stock market, a senior police officer said on Thursday.
Thai stocks .SETI plunged a combined 7.2 percent on Oct. 14-15 as rumours circulated over the health of King Bhumibol Adulyadej, although they rebounded 3.5 percent the following day.
Police Major General Panya Mamen, a deputy chief at the Central Investigation Bureau, told Reuters the police were focusing on four or five people who may have spread the rumours, which caused the biggest two-day drop this year on the bourse.
"We're now gathering all the evidence and next week the police will be applying for warrants from the Criminal Court," Panya said.
The court could issue arrest warrants or may order the individuals to turn themselves in for questioning.
"These people will be charged with violating Article 14 of the 2007 Computer Offence Act covering the posting of false computerised information that causes harm to national security and the general public," he said.
The health of the king is a sensitive topic in financial markets because he is seen as the sole unifying figure in a politically polarised country with a long history of coups and upheaval.
Thai Prime Minister Abhisit Vejjajiva said he understood four people were involved. "Police have information on this issue and if the evidence is clear, they would likely have to proceed with the case," he told reporters.
The king was admitted to hospital on Sept. 19 with a lung infection and fever and has been seen only once in public since then, on Friday, Oct. 23, when he visited royal monuments in the hospital.
The Department of Special Investigation (DSI), which comes under the Justice Ministry, is also conducting an inquiry into possible stock trading irregularities, which it expects to complete in late November.
DSI Secretary-General Tarit Pengdit told Reuters it had received information involving trading irregularities from the stock regulator on Monday and its Bureau of Financial and Banking Crime was now investigating.
"We're trying to get to the bottom of it. We hope we can conclude this case within 30 days. We want it to be fast because investors and the public are interested," he said.
Finance Minister Korn Chatikavanij said on Wednesday he would meet with the Securities and Exchange Commission (SEC) and the Stock Exchange of Thailand (SET) on Nov. 2 to look at ways of managing volatility on the stock market.
SET President Patareeya Benjapolchai said it was possible that the "circuit breaker" that triggers a half-hour halt in trading could kick in when the index falls 5 percent rather than 10 percent as at present.
The SEC has said it was seeking trading information on two accounts from two foreign brokers, Credit Suisse in Hong Kong CSGN.VX and UBS in Singapore UBSN.VX, in connection with this month's market plunge and was also looking at one domestic account. [ID:nBKK116990] (Reporting by Ploy Ten Kate and Chalathip Thirasoontharakul; Editing by Alan Raybould and Bill Tarrant)