BAGHDAD, (Reuters) – The eldest son of Abdul-Aziz al-Hakim, one of Iraq’s most powerful Shi’ite leaders, was detained near the Iranian border because members of his convoy were acting suspiciously, the U.S. military said on Saturday.

Ammar al-Hakim’s detention on Friday could strain good relations between Washington and his father’s Supreme Council for the Islamic Revolution in Iraq (SCIRI), the dominant political party in the Shi’ite-led government.

U.S. 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 U.S. 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 U.S. ambassador Zalmay Khalilzad sought to contain any political fallout by saying “we do not mean any disrespect” to the family.