Estonian Defence Minister Hanno Pevkur believes it will be challenging for Ukraine to receive an invitation to join NATO at the Alliance's upcoming summit in Vilnius.

"Inviting Ukraine to join may be challenging. The war is not over yet. Estonia is asking for a clear roadmap for Ukraine. This is something that NATO ambassadors are formulating and preparing on a daily basis. We hope that it will be ready for Vilnius. If not, then it is quite possible that the heads of state will start to finalise it on the spot," the Estonian minister said in an interview with Estonian news agency Vikerraadio, citing Estonian media outlet ERR.

He added that Estonia would go to Vilnius with a proposal that NATO member states' national defence spending should be more than two percent of their respective GDP.

"This level should be a bottom line, not a goal," Pevkur said.

Earlier, President Volodymyr Zelenskyy urged his US counterpart Joe Biden to invite Ukraine to join NATO now, even if the country joins the Alliance after the war.

Lithuanian President Gitanas Nausėda said that it would be possible to agree on commitments to Ukraine at the NATO summit in Vilnius that would not disappoint it.

Read also: Appeal of Ukrainian Civil Society Organizations to NATO Leaders ahead of Vilnius Summit