Kuwaiti police have fired tear gas and stun grenades to disperse hundreds of protesters in the capital demanding the release of Musallam al-Barrak, an opposition leader, and a purge of corrupt judges.
More than 2,000 people marched on Sunday from Kuwait City's Grand Mosque after evening Ramadan prayers and into the old market, where police broke up the demonstration.
A picture was circulated on social media of activist Abdulhadi al-Hajeri in the back of an ambulance in a blood-soaked garment.
Hadeel Bugrais, a human rights activist , told the AP news agency that Hajeri was wounded when a tear gas canister hit him in the head.
Burgais said dozens of protesters were arrested. She accompanied several lawyers to a police station to check on those arrested.
Sunday marked the fourth consecutive day that police have used tear gas to break up anti-corruption protests.
Kuwait has the most politically empowered parliament among the Gulf Arab states, with opposition politicians often directly challenging government officials over corruption and power abuses.
A brief statement by Kuwait's interior ministry said the protest was dispersed by police and that no injuries were immediately recorded. The statement made no mention of arrests, saying only that the protest was unauthorised.
The protesters are demanding the release of Barrak, who was detained in an investigation into allegations he insulted the judiciary.
Barrak revealed documents he alleges prove huge sums of illicit financial transfers were made to senior officials, including judges.
Barrak, who draws support from some of Kuwait's powerful tribes, was sentenced to jail for insulting the emir in 2013.
His arrest and conviction triggered a series of street protests. He was later acquitted.
Kuwaiti Prime Minister Jaber Al Mubarak Al Sabah, a member of the ruling family, has dismissed the documents, saying they have no value and do not stand up to scrutiny.
Barrak's group is calling for allowing citizens to run for the prime minister's job. They are currently appointed by the emir and are from the ruling family.
Many protesters on Sunday were members of his tribe, but many others joined the call for greater government accountability and transparency.
They say they are fed up with the pace of economic development in Kuwait, which was once a main hub for tourism and investment in the region but has now been shadowed by neighbouring Qatar and the UAE.