Can u mortgage houses in Monopoly?

Can u mortgage houses in Monopoly? Unimproved properties can be mortgaged through the Bank at any time. Before an improved property can be mortgaged, all the Houses and Hotels on all the properties of its color-group must be sold back to the Bank at half price. The mortgage value is printed on each Title Deed card.

Unimproved properties can be mortgaged through the Bank at any time. Before an improved property can be mortgaged, all the Houses and Hotels on all the properties of its color-group must be sold back to the Bank at half price. The mortgage value is printed on each Title Deed card.