The official claimed that only Alliance members will take part in the event.
"Next time, perhaps, we will have more time. And we will hold high-level meetings with partners. But I don't want to speculate when these meetings will be taking place; this time, the format with partners is not foreseen", he said.
Stoltenberg also added that the open door policy in NATO is a big achievement, which allowed spread the of democracy and human rights almost all around Europe after the Cold War.
'We continue working with candidate countries, such as Georgia and Ukraine. Our message is to focus on reforms, on the improvement of Armed Forces and security services, because we believe it is the best way for Euro-Atlantic integration", he said.
Earlier, Polish leader Andrzej Duda claimed that members of the NATO summit in June are going to discuss the roadmap for Ukraine's entry to the Alliance.