The United States is expected to designate Iran's elite Revolutionary Guards Corps a foreign terrorist organisation, three U.S. officials told Reuters, marking the first time Washington has formally labelled another country's military a terrorist group.

The White House just issued the designation (no link yet).

The Islamic Revolutionary Guard Corps is a part of the general Iranian military. It was founded after the 1979 revolution in Iran to protect the state from a coup by the regular Iranian army that served under the Shah.

With some 125,000 men during peacetime the IRGC is only about a third the size of Iran's regular military. It has a similar structure with a groundforce, a navy and an aerospace branch. The IRCG has two additional small branches that are of foreign policy interest. One is the missile force which controls Iran's medium range missiles. The other is the Quds Force, a brigade size unit with some 4,000 men trained for special operations abroad.