A Kuwaiti diplomat assaulted in front of his country's embassy in Iran arrived home for a medical checkup and was greeted at the airport by foreign minister.
Mohammed al-Zobi, the second secretary at the Kuwaiti embassy in Tehran, had bruises on his forehead and nose. He said the embassy had been "besieged" at one point on Tuesday, but did not provide any other detail on his assault.
The diplomat's beating up "was not an attack on an individual, it was an attack on Kuwait, and Kuwait is very angered by what happened," Foreign Minister Sheik Mohammed Al Sabah told reporters at the airport.
Sheik Mohammed accused the perpetrators of seeking to "undermine Kuwaiti-Iranian ties." He hoped the attack was an isolated incident and that the perpetrators would be found and prosecuted.
A Kuwaiti official told The Associated Press that the diplomat was attacked Tuesday by "six people who beat him severely," but said authorities did not know who was behind the assault.
The official who spoke on condition of anonymity because he was not authorized to talk to the press.
Iranian Foreign Ministry spokesman Mohammad Ali Hosseini said Wednesday that Tehran "regrets the incident" and that the attack was under investigation.
Kuwait's Foreign Ministry summoned the Iranian ambassador to protest the beating, which "does not, in any way, reflect the nature of bilateral relations," the official Kuwait News Agency reported Tuesday.
It said the Iranian ambassador, Ali Jannati, "expressed regret for the attack and promised to follow up and investigate the issue."
Kuwait's relations with the Islamic Republic deteriorated during the 1980-88 Iran-Iraq war because of Kuwait's support for Baghdad.
But Iran's neutral stand during the 1991 Gulf War that ended Iraq's brief occupation of this small oil-rich state brought the two nations closer.
The Kuwaiti government calls for a peaceful solution to the nuclear standoff between Tehran and the West. It has recently said it would not allow the United States military, which has bases in Kuwait, to use its territory to attack Iran.