Kuwait's public prosecutor has extended the detention of a prominent former opposition MP arrested on Monday.
A lawyer for Mussallam al-Barrak said he would be detained for 10 days pending further investigation.
He was questioned for five hours on Tuesday on suspicion of "undermining the status of the emir" in a speech at an opposition protest on 15 October.
Mr Barrak warned Sheikh Sabah Al Sabah that he would not be allowed to "take Kuwait into the abyss of autocracy".
The opposition feared the emir might try to change he electoral law before the forthcoming parliamentary elections, which he later did.
A decree issued by Sheikh Sabah on 19 October reduced the number of votes cast by each Kuwaiti from four to one, and reportedly made it harder for opposition groups to build coalitions.
The opposition reacted by announcing it would boycott the elections for the National Assembly scheduled for 1 December, and organising a protest on 21 October that saw tens of thousands take to the streets.
At least 29 protesters and 11 policemen were wounded as security forces broke up the demonstration with tear gas and stun grenades. The government subsequently banned gatherings of more than 20 people.
'Immune and inviolable'
At an opposition demonstration outside parliament in Kuwait City's Erada Square two weeks ago, Mr Barrak shocked many observers by publicly challenging the emir in a speech.
"We will not allow you, your highness, to take Kuwait into the abyss of autocracy," he said. "We no longer fear your prisons and your riot batons."
His remarks drew chants of "We will not allow you, we will not allow you" from the crowd.
On Monday evening, state security personnel went to Mr Barrak's home and presented to an arrest warrant issued by the public prosecutor.
He was told he was suspected of undermining the status of the emir and on Tuesday was taken to the palace of justice for interrogation. The move prompted opposition supporters to gather in Erada Square to demand his release.
On Wednesday morning, Mr Barrak's lawyer, Mohammed Abdul Qader al-Jassem, told the AFP news agency that the public prosecutor had ordered his client to be remanded in custody pending investigation and transferred him to the central prison.
Later, one unconfirmed report said Mr Barrak had been charged and citied an official as saying he had violated laws and committed libel.
Although Kuwait allows more freedom of speech than some other Gulf states, the emir is considered "immune and inviolable" in the constitution.
Three other former MPs have been detained on similar charges and freed on bail pending trial, scheduled to start on 13 November.
Mr Jassem, who is also an opposition activist, was himself accused by the Kuwaiti foreign ministry of "unacceptable interference" after he wrote a blog on Tuesday telling Saudi Arabia and the UAE to stay out of his country's affairs. Both sent troops to Bahrain last year.
"If Kuwait's 'democracy' failed to move to your countries over the past five decades, the movement for change, marches and demonstrations and protests may be easier, and it will not take a long time," he wrote.