Tensions have been high in the Maldives after weekend protests over the death of a man who opposition parties allege was killed in police custody.
The MDP says this photo shows police assaulting one of its leaders
Hussain Salah's body was pulled from a harbour in the capital on Sunday.
The opposition Maldivian Democratic Party (MDP) says he was beaten to death in custody, a charge officials deny.
The Maldives government has been under pressure over its human rights record in recent years and legalised opposition parties only in 2005.
Negotiations between the authorities and the opposition saw a number of opposition figures released from jail last year.
But the MDP now says preparations for landmark multiparty elections due in 2008 are taking too long.
The government says Mr Salah was arrested on drugs charges and died after he was released on Friday.
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It said "unruly crowds" of opposition supporters had roamed the streets. There had been a number of arrests.
"MDP supporters also created unrest... A number of police constables were injured as the violent mob hurled stones and projectiles, and torched public property. Some of the injuries were serious," a statement from chief government spokesman Mohamed Shareef said.
The MDP said one of its senior leaders, Mohamed Nasheed, had been badly beaten by police and then briefly detained following the disturbances.
He was freed early on Monday morning.
Mr Nasheed was among several hundred people who gathered at a cemetery to pay their respects to Mr Salah on Saturday.
His party says it has evidence the dead man was still in jail on that day, contrary to the official version of events.
"His cell mates... people around him [in detention] noticed him on the 14th and some of them have given us evidence that he was beaten and he was shouting," acting MDP president Ibrahim Hussain Zaki told Reuters news agency.
In September 2003 anti-government riots rocked the Maldives capital when news emerged that two inmates had died in a jail riot.
The mayhem was unprecedented in the Maldives, a tranquil Indian Ocean atoll famed for its upmarket tourist resorts.