MADRID, June 29 (Reuters) - NATO Secretary-General Jens Stoltenberg said on Wednesday he expected a swift ratification of Sweden and Finland's membership of the military alliance.

"We will make a decision at the summit to invite Sweden and Finland to become members, that's unprecedented quick," he told reporters on the second day of a NATO summit in Madrid. Both countries applied for membership of the alliance in mid-May.

"After invitation, we need a ratification process in 30 parliaments," he added. "That always takes some time but I expect also that to go rather quickly because allies are ready to try to make that ratification process happen as quickly as possible."