(Adds prosecutor's demand, Yildirim questioning, shares)
* Fenerbahce chairman exercises right to silence
* PM Erdogan says Turkey's image stained
* Trabzonspor shares surge on title speculation
By Daren Butler
ISTANBUL, July 7 (Reuters) - A Turkish court jailed 15 more people, including top soccer club executives, pending trial on Thursday as part of a major match-fixing investigation which the prime minister said is staining the country's image.
Three executives of champions Fenerbahce, the chairman of Sivasspor and coach of Eskisehirspor were among the 15 sent to jail on the orders of an Istanbul court, state-run Anatolian news agency reported.
The investigation has thrown preparations for the new season into disarray just a month before kick-off and the Turkish Football Federation is expected to act soon in response to the allegations without waiting for the outcome of the case.
Among possible sanctions are exclusion from competitions, relegation to a lower division and potentially the loss of tens of millions of dollars in income. Any individuals convicted of match-fixing could face lengthy prison sentences.
A total of 22 have now been jailed after seven were sent to Metris prison on Wednesday and prosecutors on Thursday called for another three people to be remanded in custody while releasing a further eight people, TV channels reported.
Shares in Fenerbahce , the wealthy Istanbul club which won the league for a record 18th time last season, have lost a third of their value since news of the police raids emerged.
Fenerbahce have denied involvement in any wrongdoing.
Shares in Trabzonspor , runners-up last season, surged 17 percent, bringing gains in the last three days to 40 percent, on speculation the league title could be awarded to them.
Istanbul police headquarters said in a statement on Wednesday it had seized eight unlicensed guns in the raids after a probe launched in December produced evidence of match-fixing in 19 games in the first and second divisions.
Out of 61 people detained in raids launched early on Sunday 35 have now been released leaving the 22 jailed pending trial and the three prosecutors have asked to be held in custody.
The most high-profile detainee, Fenerbahce chairman Aziz Yildirim, was sent to police headquarters on Thursday after being treated in hospital for suspected heart problems.
Broadcaster CNN Turk said he was exercising his right to silence in police questioning. He is expected to attend court on Friday for a ruling on whether he will be jailed.
Among others in jail are Sivasspor's goalkeeper, a former international striker, and the former chairmen of Diyarbakirspor and Giresunspor.
Prime Minister Tayyip Erdogan, himself a Fenerbahce fan and member of its congress, has called for a rapid and just outcome to the investigation, saying the affair was staining the country's image internationally.
European soccer's governing body UEFA has set a deadline of July 15 for confirmation of the team taking part in the third Champions League qualifying round. Trabzonspor were runners-up to Fenerbahce in the league and would normally take that place.
Police launched raids in 15 provinces across Turkey on Sunday, searching club premises and detaining players and administrators in connection with the scandal.
Turkish media have cited allegations in police reports such as a striker being offered money to not score in one game, a goalkeeper deliberately failing to prevent a goal and a club requesting a particular referee for a key derby. (Editing by Peter Rutherford and Pritha Sarkar)