It is up to Ukraine to decide what terms are acceptable for negotiations to bring an end to the war Russia is waging against the country, NATO Secretary General Jens Stoltenberg said on Monday, adding NATO's role was to support Kyiv.

"It is for Ukraine to decide what kind of terms are acceptable. It is for us to support them," he said during a press conference with members of the Dutch government in The Hague.

"We should not make the mistake of underestimating Russia (...) They still control large parts of Ukraine (...) What we should do is strengthen Ukraine's hand," Stoltenberg added.