Aboard Air Force One: President Joe Biden and his Turkish counterpart Recep Tayyip Erdogan are expected to hold talks Wednesday on the sidelines of the NATO summit in Madrid, a US official told reporters Tuesday.

"We do expect at some point tomorrow that President Erdogan and President Biden will have a chance to talk," National Security Advisor Jake Sullivan said aboard Air Force One.

Turkey's opposition to Finland and Sweden entering the western military alliance is a hot topic at the summit, but Sullivan said the United States was not adopting a "brokering role" and would leave the NATO secretary general in charge.