Ukraine's aspirations to join NATO and the European Union are envisaged in its constitution and remain the country's absolute priority, President Volodymyr Zelenskyy's spokesperson said on Monday responding to a Ukrainian ambassador's reported comments. Meanwhile, in a separate statement, the president himself has also underlined that Ukraine is "still seeking NATO membership."

Ukraine's Ambassador to Britain Vadym Prystaiko was also quoted by the BBC as saying Kyiv was willing to be "flexible" over its goal to join the Atlantic military alliance, a move Russian President Vladimir Putin has said would be a trigger for war.

"This course is not only reflected in the Constitution, but is also the full consent of the authorities and society," presidential spokesperson Sergii Nykyforov told Reuters. "Mr. Ambassador used the word 'flexibility.' I think it's worth giving him the opportunity to explain what exactly he had in mind."

Prystaiko clarified earlier remarks, saying that the former Soviet republic would not be reconsidering its attempt to join the military alliance.

Asked whether or not Ukraine might reconsider its ambitions to join NATO, Prystaiko told the BBC in English: "No this is not and I am quite happy that I have this chance to clarify my position."

Prystaiko said the earlier BBC report was the result of a misunderstanding.

"We are not a member of NATO right now and to avoid war we are ready for many concessions and that is what we are doing in conversations with the Russians," Prystaiko said. "It has nothing to do with NATO which is enshrined in the constitution."

"It is not a delay to our ambitions to be in NATO - what we are talking about is that we are not in the family now so we have to look for something else like bilateral agreements with the UK, with the United States," he said. "So on top of NATO we are looking for some other arrangements which would allow us to survive at this particular ordeal right now."

Asked again if Ukraine was shifting its bid to become a NATO member, he said: "No."

Ukraine is not a NATO member but has a promise dating from 2008 that it will eventually be given the opportunity to join, a step that would bring the U.S.-led alliance to Russia's border.

Putin says Ukraine's growing ties with the alliance could make it a launchpad for NATO missiles targeted at Russia. He says Russia needs to lay down "red lines" to prevent that.

Russia has moved more than 100,000 troops and heavy weapons to within striking distance of Ukraine in recent weeks, prompting the United States and its NATO allies to warn that an invasion could be imminent.

Moscow denies it is planning an attack, calling the military maneuvers exercises, but it has issued written demands that NATO forgoes any further expansion eastwards including Ukraine. NATO members have rejected the demand.

U.S. President Joe Biden spoke to his Ukrainian counterpart Zelenskyy on Sunday and agreed to continue diplomatic efforts to try to resolve the crisis, the White House said.