Poland's Vice Premier, Jaroslaw Kaczynski, suggested a peacekeeping deployment in Ukraine to provide humanitarian aid during a visit to Kyiv on Tuesday.

But NATO defence ministers were wary over the idea as they arrived in Brussels for urgent talks on Russia's war against its neighbour.

"I'm afraid we're still in too early stages to talk about that," said Dutch Defence Minister Kajsa Ollongren.

"First we have to have a ceasefire. We have to see a withdrawal from Russia. There has to be some kind of agreement between Ukraine and Russia, and I think the talks are still going on."

She added: "It's always good to think about what comes after that, but first, we need to achieve that."

Estonian Defence Minister Kalle Laanet said that a proposed peacekeeping mission was "one of the possibilities and, of course, we have to look to all the possibilities which can help Ukraine".

But he said a deployment would need the backing of the United Nations Security Council where Russia holds a veto.

Britain's defence minister Ben Wallace said he would need to "look at the details first before making any decisions about what happens".

NATO has rebuffed pleas from Ukraine to intervene in the conflict, including imposing a no-fly zone to help halt Russian bombings.

The US-led alliance says its direct involvement in non-member state Ukraine could spark a confrontation with Russia that may spill over into nuclear war.

NATO allies have instead been sending weapons to help Ukrainian forces to defend their country, especially vitally needed portable anti-tank and anti-aircraft missile systems.

Moscow has warned that any deliveries are legitimate targets for its military to strike.

But NATO defence ministers insisted they would keep arms flowing to Ukraine.

"We support their ability to defend themselves and we'll continue to support them going forward," US Secretary of Defense Lloyd Austin said.