Baghdad - Iraqis took to the streets of Shi'ite towns and cities on Saturday to protest over the detention by US troops of the eldest son of Abdul-Aziz al-Hakim, one of Iraq's most powerful Shi'ite leaders.

There were no reports of violence. The US military said Ammar al-Hakim was held on Friday because members of his convoy were acting suspiciously at a border checkpoint while returning from Iran.

The incident could strain good ties between Washington and the elder Hakim's Supreme Council for the Islamic Revolution in Iraq (SCIRI), the dominant party in the Shi'ite-led government.

SCIRI supporters held protests in Najaf, Kerbala, Basra, Kut and other towns in the mainly Shi'ite south of Iraq, witnesses and local media said.

US military spokesman Lieutenant-Colonel Christopher Garver said in a statement the convoy was stopped because the vehicles met "specific criteria for further investigation in an area where smuggling activity has taken place in the past".

"At the time, members of the convoy did not cooperate with Coalition Forces and displayed suspicious activities which subsequently led to Mr. Hakim's detention," Garver said.

"Further investigation led to Mr. Hakim's release to Iraqi authorities and the return of his possessions. Mr. Hakim was treated with dignity and respect throughout the incident.

"Unfortunate incidents such as this occasionally occur as Iraq endeavors to secure its borders," he said.

Washington accuses Iran of providing weapons to Shi'ite militias in Iraq. Security forces closed the border with Iran for several days earlier this month.

Ammar al-Hakim told reporters on Friday US troops said his passport had expired. He said the document was valid.

"The way I was arrested was disrespectful and not appropriate for a political and religious figure like me. They cuffed my hands and blindfolded my eyes. They raised their weapons against me," he said after his release.

Hakim was released within hours and US ambassador Zalmay Khalilzad sought to contain any political fallout by saying on Friday "we do not mean any disrespect" to the family.

"American Foolishness"

Up to 1,000 protesters gathered in Iraq's second biggest city, Basra, marching through the streets and chanting "Death to America" and "Death to Britain".

Abdul-Kareem al-Jazairi, Abdul Aziz al-Hakim's Basra representative, said the incident highlighted "American foolishness".

"He is a well-known figure and to claim he was arrested by mistake is nonsense. We consider this an American attempt to create chaos in Iraq," he said.

Demonstrations in Kerbala and Najaf also drew hundreds of people, and the SCIRI-run television channel Furat showed footage on Saturday of protests in several other towns.

US forces have recently arrested a number of Iranians in Iraq, including several who were seized at Abdul-Aziz al-Hakim's compound in Baghdad. They were later released.

SCIRI was founded in Iran in 1982 and its continued links to Shi'ite Islamist Iran are a source of concern for Washington, which accuses Iran of fuelling violence in Iraq.

SCIRI's military wing, the Badr Organisation, fought with Iran in the 1980-88 war against Saddam Hussein, ousted in 2003 by a US-led invasion. Sunni leaders accuse it of targeting members of the minority sect, a charge Hakim denies.

US and Iraqi forces launched a major security crackdown in Baghdad this month, vowing to deal even-handedly with Shi'ite militias as well as Sunni Arab insurgents.

Washington has courted the elder Hakim in its efforts to stabilise Iraq and create a moderate Shi'ite bulwark against the growing influence of radical anti-American Shi'ite cleric Moqtada al-Sadr. The elder Hakim held talks with US President George W. Bush in Washington in December.