Turkey's President Tayyip Erdogan shakes hands with NATO Secretary General Jens Stoltenberg in Istanbul. (Photo: Reuters)

He also said officials from Turkey, Sweden and Finland would meet later this month for talks to try to overcome objections from Turkey and Hungary that have delayed Sweden's NATO membership bid. 

Turkey in March ratified Finland's bid for membership of the North Atlantic Treaty Organization, but still objects to Sweden joining the alliance, as does Hungary.  

In its objections to Swedish membership, Turkey has said Stockholm harbours members of militant groups it considers to be terrorists.

“Sweden has taken significant concrete steps to meet Turkey's concerns,” Stoltenberg told reporters, referring to a constitutional change by Sweden and its stepping up of counter-terrorism cooperation with Ankara.