Kuwaiti police fired teargas and stun grenades to disperse an opposition rally demanding the release of prominent dissident Mussallam al-Barrak, activists said on Thursday.
The public prosecutor on Wednesday ordered Barrak, a former MP, to be held for 10 days after he was questioned for allegedly insulting the judiciary.
Thousands of people gathered at Barrak's residence southwest of Kuwait City on Wednesday night and marched on the nearby jail where the former opposition leader was detained, the activists said.
Police intervened when hundreds of protesters reached the prison, firing teargas and stun grenades to disperse them. There were no reports of any casualties.
Smaller protests were also reportedly staged in other parts of the oil-rich Gulf state.
Kuwaitis hold rallies at night because of soaring temperatures during daylight hours in the desert country. Muslims are also observing Ramadan, the month of fasting where eating and drinking is prohibited during the day.
Barrak's lawyer Thamer al-Jadaei is expected to file a petition Thursday to demand the detention period be scrapped.
The opposition leader was accused of slandering and insulting the supreme judicial council and its chairman, Faisal al-Marshed, in remarks made at a public rally on June 10.
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Opposition groups strongly criticised the action taken against him, saying it was unlawful and "politically motivated".
At the rally, Barrak claimed former senior officials, including members of the ruling family, had stolen tens of billions of dollars from public funds and engaged in money laundering.
He also criticised the judiciary.
The scandal was later linked to claims 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.
Sheikh Ahmad is scheduled to be questioned on Thursday by the public prosecutor as a witness.
The claims plunged Kuwait into a political crisis that prompted the emir to call for calm and let the judiciary handle the issue.
Most opposition groups are not represented in parliament after boycotting a July 2013 election 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.