Ukrainian President Volodymyr Zelenskyy also urged NATO leaders to immediately approve the uncontested parts of Ukraine for membership.

Ukrainian Foreign Minister Andrii Sybiha has urged his NATO counterparts to issue an invitation during a meeting in Brussels next week to Kyiv to join the Western military alliance, according to the text of a letter seen by Reuters on Friday.

"We believe that the invitation should be extended at this stage," Foreign Minister Andrii Sybiha wrote in a letter to his NATO counterparts.

The BBC's Analysis Editor looks at what we know about the claims that North Korean troops are involved in the war in Ukraine.

North Korean leader Kim Jong Un told Russian defence minister Ukraine's use of long-range weapons is the result of direct military intervention by the United States and Moscow is entitled to take action in self-defence,

Russian Defense Minister Andrey Belousov visited North Korea. Ukrainian media suggest that discussions may once again focus on the support Pyongyang provides to Moscow. They remind us that the scale of arms supplies to Putin's army is already significant.

Russian forces have launched a major assault on Ukraine, firing missiles on cities and military targets. The invasion by land, air and sea began after a pre-dawn TV address where Russian President Vladimir Putin demanded that Ukraine's military lay down its arms.