Tehran: Iran has complained to UN Secretary-General Ban Ki-moon about the arrest by US troops of five Iranian diplomats, who Washington says were helping militants in Iraq, state television reported on Saturday.

US soldiers seized the men in a raid on an Iranian government office in the northern Iraqi city of Arbil on January 11, hours after US President George W. Bush pledged to crack down on the "flow of support" from Iran to Iraqi militants.

"Iran officially complained, by sending a letter to the UN Secretary-General, about America's abduction of Iranian diplomats in Arbil," state television said.

The letter said the arrests were illegal and called for a response from the UN Security Council.

"The Islamic Republic of Iran holds America responsible for the consequences of this act and demands the immediate release of the consulate officers," the letter read, according to the television station.

Iran's official news agency IRNA quoted the Iranian ambassador to Baghdad, Hassan Kazemi Qomi, as saying the Iraqi government had given assurances that the five diplomats would be released this week, the official IRNA news agency reported on Saturday.

"The Iraqi government has assured that five Iranian diplomats kidnapped in Arbil will be released this (Iranian) week (ending Friday)," IRNA quoted Hassan Kazemi Qomi as saying.

"The host country is responsible for protecting diplomatic missions, so the Iraqi government has been trying to free the five diplomats since the first hours of the incident," he said.

Iraqi Foreign Minister Hoshyar Zebari has said that the five Iranians had been working in Arbil with official sanction, but that their "liaison office" had not yet become a full consulate.

The arrests on January 11 were the second such detentions in Iraq in a month, and have further heightened tensions between Washington and Tehran, which are at loggerheads over Iran's nuclear programme.