In a statement released by the ministry's media department, Foreign Ministry spokesman Mohammad Ali Hosseini called it as an "interventionist act" by the U.S. forces to arrest "members of an Iranian technical delegation" in their hotel in Baghdad on Tuesday evening.

"The ministry summoned the Swiss charge d'affaires to express its strong protest to U.S. behavior which is against the international laws and regulations and asked for explanations," said Hosseini.

"This action was inconsistent with the responsibilities of foreign forces in Iraq and it could be another mistake for the United States," he stressed, adding the detainees had been released Wednesday morning.

The spokesman said the detainees were experts from Iran's energy ministry and were invited by the Iraqi government to discuss building a power plant in the war-torn country.

The Iranian delegation was stopped by U.S. troops Tuesday evening in a hotel in Baghdad and eight Iranians were taken away.

According to the U.S. military, the Iranians were seized because unauthorized weapons such as AK-47 assault rifle and 9mm pistols were found in their cars.

Later in the hotel, the U.S. forces also seized a laptop, cell phones and a bag full of Iranian and American money.

This was the second time that U.S. troops captured Iranians in Iraq.

In January, five Iranians were detained in Iraq's northern city of Arbil under charges of assisting insurgents to fight with coalition forces but Tehran denied the U.S. accusations. The five men were still in the custody of the United States.