"We are always concerned. We know who Putin is. We know who our neighbor is and what we can expect. That is why we taking this meeting and its possible results very seriously," the president told reporters as she arrived for NATO's summit in Brussels.

Grybauskaitė likened next week's US-Russia summit in Helsinki to Trump's "controversial" talks with North Korean leader Kim Jong Un.

"We saw another interesting meeting with North Korea's leader, where the results, I'd say, were very controversial, too," she said.