Stoltenberg made the announcement after talks with Erdogan and Swedish Prime Minister Ulf Kristersson on the eve of a NATO summit in Lithuania.
Sweden’s NATO accession has been held up by objections from Turkey since last year.
Earlier, President Erdogan on Monday introduced a new condition for approving Sweden's membership in NATO, calling on European countries to “open the way” for Turkey to join the European Union.
The surprise announcement by Erdogan before departing for a NATO summit in Lithuania's capital added new uncertainty to Sweden's bid to become the alliance's 32nd member, which Turkey initially blocked by saying Sweden was too soft on Kurdish militants and other groups that Ankara considers security threats.
It was the first time that Erdogan linked his country's ambition to join the EU with Sweden's efforts to become a NATO member.
“Turkey has been waiting at the door of the European Union for over 50 years now, and almost all of the NATO member countries are now members of the European Union,” Erdogan told reporters in Istanbul. “I am making this call to these countries that have kept Turkey waiting at the gates of the European Union for more than 50 years.”
“Come and open the way for Turkey’s membership in the European Union. When you pave the way for Turkey, we’ll pave the way for Sweden as we did for Finland,” he added.
Earlier, Erdogan's office said he told U.S. President Joe Biden during a telephone call Sunday that Turkey wanted a “clear and strong” message of support for Turkey’s EU ambitions from the NATO leaders. The White House readout of the Biden-Erdogan call did not mention the issue of Turkish EU membership.