Iran called for calm on Sunday after protests in a southern city over water shortages turned violent overnight with reports of police shooting at demonstrators who attacked banks and public buildings.
"No one has been killed in the unrest and just one person has been wounded in a shooting," said Interior Minister Abdolreza Rahmani Fazli, quoted by the state news agency IRNA.
"Our effort is to bring these protests to an end as soon as possible with restraint from police and the cooperation of authorities, but if the opposite happens, the judiciary and law enforcement forces will carry out their duties," Rahmani Fazli was quoted as saying.
Shots could be heard on videos circulated on social media from the protests in Khorramshahr, which has been the scene of demonstrations for the past three days, along with the nearby city of Abadan. The videos could not be authenticated by Reuters.
State television showed banks with broken windows and footage appearing to shows an identified demonstrator armed with a rifle.
Police fired tear gas as protesters set fire to a bridge, and to a garden surrounding a museum which is a memorial to the Iran-Iraq war in the 1980s, state media said.
A number of protests have broken out in Iran since the beginning of the year over water, a growing political concern due to a drought which residents of parched areas and analysts say has been exacerbated by mismanagement.
Oil-rich southwestern Khuzestan province, where Khorramshahr is located, is the home of many members of Iran's ethnic Arab minority, who have long complained of alleged discrimination and tight control by security forces.
Speaking before the clashes, Iranian Supreme Leader Ayatollah Ali Khamenei said on Saturday that the United States was acting together with Sunni Muslim Gulf Arab states that regard Shi'ite Muslim Iran as their main regional foe in trying to destabilise the government in Tehran.
"If America was able to act against Iran, it would not need to form coalitions with notorious and reactionary states in the region and ask their help in fomenting unrest and instability," Khamenei told graduating Revolutionary Guards officers, in remarks carried by state TV.