Kuwait's public prosecutor on Wednesday ordered opposition leader Mussallam al-Barrak to be held in custody for 10 days after he was questioned for allegedly insulting the judiciary, his lawyer said.
"The public prosecutor decided to detain Barrak for 10 days pending further investigation," one of the ex-MP's lawyers, Thamer al-Jadaei, told AFP.
"We will file a petition against the decision tomorrow (Thursday) to demand that the detention period be scrapped," he added.
The prosecutor interrogated Barrak overnight for several hours and had ordered his detention until Wednesday night for further questioning. But after reviewing the case, he issued the new decision, Jadaei said.
Under Kuwait law, the prosecutor can detain a suspect for a 10-day period that can be renewed a maximum of three times unless a judge overturns the decision.
Mohammad al-Jassem, another of Barrak's lawyers, said his client was questioned for alleged slander and insults to the supreme judicial council and its chairman, Faisal al-Marshed.
Dozens of activists and former opposition MPs gathered outside the police headquarters where Barrak was held as opposition groups called for a public rally in Kuwait City later Wednesday.
Barrak was questioned over two lawsuits filed by the judicial council and Marshed over remarks he made at a June 10 public rally that were deemed offensive.
He had claimed that former senior officials including members of the ruling family had stolen tens of billions of dollars from public funds and engaged in money laundering.
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Barrak, who also criticised the judiciary, charged that the former officials had deposited the funds in foreign banks including one in Israel.
The scandal was later linked to claims that the same officials were seen in video footage plotting a coup.
Those allegations were made in a lawsuit filed last month by Sheikh Ahmad Fahad al-Sabah, a senior ruling family member and former energy minister.
Alam Al-Youm newspaper reported on Wednesday that the prosecution service has summoned Sheikh Ahmad as a witness on Thursday to hear his testimony on the allegations.
The claims plunged the oil-rich Gulf state into a political crisis that prompted the emir to call for calm and let the judiciary handle the issue.
Before being questioned, Barrak said the public prosecutor was not impartial because he is on the judicial council which sued him.
He also said the public prosecutor should have initiated the case by interrogating the former officials who allegedly plotted the coup and stole the money.
Most opposition groups are not represented in parliament after boycotting an election last July in protest at a change to the electoral law.
OPEC member Kuwait experienced the worst domestic political turmoil in its history between mid-2006 and last year.
During that period, some dozen governments were formed and parliament was dissolved six times.