Foreign ministers from the 32-nation alliance gathered in Brussels to discuss Washington's push to end the fighting -- but US top diplomat Marco Rubio was skipping the meeting.

The gathering comes after US envoys appeared to fail to make a major breakthrough on efforts to stop the war in five hours of talks with Putin in Moscow.

"The peace talks are ongoing, that's good, but at the same time, we have to make sure that whilst they take place -- and we are not sure when they will end -- that Ukraine is in the strongest possible position to keep the fight going," NATO chief Mark Rutte said.

As part of those moves Germany, Poland, the Norway, The Netherlands and Canada said they would together commit some one billion dollars more to a scheme to buy American weapons for Ukraine.

"Ukraine needs to stay strong and we, the allies in the largest and most successful military alliance in history, need to stay firm, and we need to stay committed," Norway's Espen Barth Eide said.

Europe has largely been left of the sidelines of US President Donald Trump's push to end the war and the absence in Brussels of Rubio, who sent a deputy, risked reinforcing that impression.

A string of ministers said that Putin did not appear so far to be willing to make any concessions at talks with Washington's representatives.

"President Putin should end the bluster and the bloodshed and be ready to come to the table and to support a just and lasting peace for Ukraine," said British foreign minister Yvette Cooper.

They also pushed back against comments from the Russian president that he did not want conflict with Europe, but was "ready" for war.

"It's the rhetoric that Russia is making use of in order to intimidate us, and we shouldn't take such talks too seriously," said Finland's Elina Valtonen.

"We have very strong capabilities as NATO, as Europe, and we are ramping up by the day."