Police in Kuwait have used tear gas and stun grenades to disperse large numbers of people demonstrating against an electoral law.
Activists and medical sources said dozens of people had been injured.
There have been protests in Kuwait after the emir, Sheikh Sabah al-Ahmad al-Sabah, dissolved a parliament dominated by opposition groups.
The government called an election for 1 December with a new law that the opposition says will work against them.
Kuwait's parliament has the most powers of any elected body in the Gulf and opposition members of parliament openly criticise the ruling Sabah family.
However, the Sabahs - who have ruled Kuwait for more than 250 years - retain full control over key government and executive posts.
The 83-year-old emir is referred to as "immune and inviolable" in the constitution.
On Sunday, police tried to prevent the protesters gathering at several sites in Kuwait City, the capital, and from marching towards the government headquarters.
Activists and observers said tens of thousands of people had turned out. The authorities did not give an estimate.
Human rights lawyer Mohammed al-Humaidi said as many as 100 people had been injured. Several policemen were reportedly wounded.
At least 15 people, including a former Islamist member of parliament, were arrested.
Kuwait's stock market dropped by more than 3% on Sunday, the biggest loss on a single day since 2009.
In June, Kuwait's top court declared elections for the 50-seat parliament in February invalid and reinstated a more government friendly assembly.
That vote saw significant gains for the Islamist-led opposition.
The government announced last week that it was calling elections for December and changing the electoral law in order to "preserve national unity".