* Opposition figures arrested after critical protest rally
* MPs said to have criticised ruler of Kuwait
* Ruling family issues rare statement stressing obedience
By Sylvia Westall
KUWAIT, Oct 18 (Reuters) - Kuwait's ruling Al-Sabah family issued a rare statement on Thursday calling for obedience to the emir after a series of opposition gatherings and a large rally earlier this week.
The Gulf oil producer has seen regular demonstrations since last year, stemming from a struggle between the government dominated by the ruling family and mainly Islamist and tribal lawmakers in parliament.
But tensions have increased after Sheikh Sabah al-Ahmad al-Sabah dissolved parliament last week. Opposition figures say they fear the cabinet will try to push through new voting rules that could help pro-government candidates in an election expected later this year.
"His Highness the Crown Prince, in his capacity as President of the Council, would ... like to assert His Highness the Emir's right to be obeyed," said the statement from the Al-Sabah family council published on state news agency KUNA's English service.
It cited a Koranic verse calling on believers to obey the Prophet "and those charged with authority among you".
Kuwaiti authorities arrested two opposition politicians earlier on Thursday and interrogated a third after they made comments seen as criticising Sheikh Sabah, an interior ministry official said.
The former members of parliament spoke at an opposition-led rally of about 5,000 people on Monday where Kuwaitis later clashed with riot police close to parliament.
The men had also spoken at opposition gatherings before Monday's rally. It was not immediately clear which remarks were deemed illegal.
The Al-Sabah dynasty has ruled Kuwait for more than 250 years. The 83-year-old emir has led the country since 2006.
Although Kuwait allows more freedom of speech than some of its fellow Gulf states, the emir is seen as untouchable and is referred to as "immune and inviolable" in the constitution.
Former lawmakers Bader al-Dahum and Falah al-Sawwagh were taken into police custody, the interior ministry official said. Khaled al-Tahus, also a former MP, was summoned for questioning by the prosecution service.
However Musallam al-Barrak, a prominent opposition figure, had not been arrested. He had appealed directly to the emir on Monday to avoid "autocratic rule" in a strong speech analysts said could provoke a firm reaction from authorities.
"The (family) council would like to reaffirm that any affair relating to the ruling family is not subject to publication in any form whether audio, visual or written," the Al-Sabah statement said.
It referred to recent media reports that members of the family had tendered "a note" to the emir, but gave no details.
KUNA issued English and Arabic versions of its report. An additional comment in Arabic said the Crown Prince, the emir's 75-year-old brother and leader-in-waiting, also stressed that the council "always plans its steps under the direction of the emir".
Sheikh Sabah has the final say in state matters and he picks the prime minister who in turn selects a cabinet, with major portfolios held by Al-Sabah family members.
A group of around 500 people gathered outside the Justice Palace late on Thursday to protest against the detention of the former lawmakers.
"We are here because the three National Assembly members are inside as well as four other people," Ahmed al-Sawwagh, cousin of one of the detained politicians, said.
The four other people he was referring to were demonstrators who were arrested on Monday after the protest rally. One of those being held is the son of prominent opposition politician Ahmed al-Saadoun, a former parliament speaker.