Iran has sent an official letter of complaint to U.N. Secretary-General Ban Ki-moon demanding action against the United States for its recent arrest of five Iranians in Iraq.

The Iranian letter strongly condemns the January 11 raid by U.S. forces on an Iranian office in the northern city of Irbil as an "illegal, flagrant violation of the basic principles of international law and diplomatic conventions."

Iran has demanded the immediate release of the five men that Tehran officials say are diplomats who were engaged in legal activity in Iraq when they were arrested.

The U.S. military says the five Iranians were involved in arming Iraqi insurgents.

Iran's letter to the U.N. calls for "an urgent" response from the Security Council, of which the United States is one of five a permanent members with veto power.

Meanwhile, Iran's state news agency, IRNA, Saturday quoted Iran's ambassador to Iraq, Hasan Kazemi Qomi, as saying the Iraqi government has assured him the five Iranian detainees will be released by next Friday.

The United States has accused Iran of meddling in Iraq.

Some information for this report was provided by AFP and Reuters.