BAGHDAD , Iraq ( CNN ) -- Iraqi President Jalal Talabani has blasted the United States for the arrest Thursday of an Iranian and called for his immediate release . Iraqi President Jalal Talabani says an Iranian detained by the U.S. was a civil servant on a trade mission . The U.S. military said the detainee is a member of an elite Iranian unit that has been accused of training and equipping insurgents in Iraq , but Talabani said he is a civil servant who was on an official trade mission in Iraq 's Kurdistan region . The `` letter of resentment '' was dated Thursday and addressed to Ryan Crocker , U.S. ambassador to Iraq , and Gen. John Petraeus . Presumably , the Iraqi president was referring to U.S. Gen. David Petraeus , commander of multinational forces in Iraq . Iraqi and Kurdish regional government representatives were aware of the man 's presence , Talabani wrote . As a result of the incident , Tehran threatened to close its border with the Kurdistan region unless the detainee , identified as Agay Mahmoody Farhadi , is released . Closing the border would cause `` severe damage to markets and trade in the province on this blessed month , '' Talabani said , referring to Ramadan . `` Therefore , I express to you our outrage for these American forces arresting this Iranian civil official visitor without informing or cooperating with the government of the Kurdistan region , which means insult and disregard for its rights , '' he wrote . `` I call for his release immediately in the interest of the Iraq Kurdistan region and the Iranian-Iraqi relations . '' The detainee belongs to Iran 's Islamic Revolutionary Guards Corps-Quds Force , `` a covert action arm of the Iranian government responsible for aiding lethal attacks against the Iraqi government and coalition forces , '' the U.S. military said . The military said the man `` has been involved in transporting improvised explosive devices and explosively formed penetrators into Iraq . Intelligence reports also indicate he was involved in the infiltration and training of foreign terrorists in Iraq . '' He is one of several Iranians in U.S. custody in Iraq . E-mail to a friend .
In letter , Jalal Talabani says detainee is civil servant on trade mission . U.S. military says man belongs to elite unit that trains , equips insurgents . Man was merely doing business in Kurdistan region , Talabani says . Iran threatens to close border , which would harm trade , he says .