If a third party should attempt to carry out a policy of usurpation by means of armed intervention in Persia, or if such Power should desire to use Persian territory as a base of operations against Russia, or if a Foreign Power should threaten the frontiers of Federal Russia or those of its Allies, and if the Persian Government should not be able to put a stop to such menace after having been once called upon to do so by Russia, Russia shall have the right to advance her troops into the Persian interior for the purpose of carrying out the military operations necessary for its defence. Russia undertakes, however, to withdraw her troops from Persian territory as soon as the danger has been removed.