Foreign ministers from the alliance will meet in Brussels on Nov. 28-29 and Turkey's parliament has begun debating the instrument giving Turkey's approval, which is needed for Sweden to become a member.

"It's up to (Turkey) whether their system will produce the consent in that time frame, but we're continuing to speak with them about that," said the U.S. official, who briefed reporters on condition of anonymity.

(Reporting by Simon Lewis; Editing by Chizu Nomiyama)