"NATO will give Ukraine security, Ukraine will make NATO stronger," said Zelensky, standing alongside Lithuanian President Gitanas Nauseda, before a Ukrainian army flag from the key battleground of Bakhmut was raised.

An eastern Ukrainian city once known for its salt-mining and sparkling wine, Bakhmut has been razed to the ground in the longest and bloodiest battle of the war.

"Bakhmut is one of the most decisive battles for freedom in Europe, and that is how our children and grandchildren will remember it," Zelensky said.

Zelensky is set to push NATO members for a clear timetable on bringing his country into the alliance -- even if he had said he does not expect Ukraine to join before the end of the war.

"Today I set off here with faith... in a NATO that does not hesitate, does not waste time," Zelensky said.

"I would like this faith to become confidence -- confidence in the solutions that we deserve," Zelensky said.

Kyiv and NATO members in eastern Europe believe only bringing Ukraine under the alliance's collective defence umbrella will deter Moscow.

Key powers like the United States and Germany have been wary of going much beyond a vow in 2008 that said Ukraine will join one day, without setting a timeframe.