The trip comes as pressure builds on Erdogan to drop his opposition to Sweden joining NATO.

Stoltenberg on Thursday said during a NATO foreign ministers' meeting in Norway that he would soon visit Ankara to work towards Sweden joining "as early as possible", after speaking with Erdogan by phone earlier this week.

The NATO statement said Stoltenberg would attend Erdogan's inauguration on Saturday. The Turkish president was last week re-elected to serve another five-year term.

The statement said the visit would extend into Sunday and Stoltenberg would "have bilateral meetings with President Erdogan and with senior Turkish officials".

NATO member Turkey has dragged its feet over admitting Sweden to the military alliance. It and Hungary are the only two member countries yet to ratify Sweden's membership bid.

Finland formally joined the alliance in April.

Erdogan has accused Sweden of being a haven for "terrorists", especially members of the Kurdistan Workers' Party (PKK).

Swedish Foreign Minister Tobias Billstrom on Thursday said his country has fulfilled all its commitments to join, and "it is time for Turkey and Hungary to start the ratification of the Swedish membership to NATO".

Many of the ministers who attended the Oslo meeting said they wanted to see Sweden join before a NATO summit in Lithuania's capital Vilnius on July 11-12.

Stoltenberg has said that goal is "absolutely possible".

US Secretary of State Antony Blinken, whose country is the dominant member of NATO, also said on Thursday that "we fully anticipate" Sweden joining by the Vilnius summit.