On the commencement of proceedings to foreclose, either by action or advertisement, any mortgage on a leasehold estate of more than three years covering urban property, or at any time after such commencement until the expiration of the period of redemption, the owner of any such mortgage or the purchaser at the foreclosure sale, as the case may be, may apply to the district court for the appointment of a receiver to take immediate possession of the mortgaged premises and to hold, maintain, and operate the same and collect the rents and income therefrom, and apply the same in the manner hereinafter specified. The application for such receiver may be included in an action to foreclose the mortgage or may be by separate action and, if by separate action, the only necessary party defendant shall be the owner of the mortgaged leasehold at the time of the commencement of the action.