BRUSSELS, Belgium -- NATO members on Tuesday urged each other not to let up in backing Ukraine's fight against Russia, amid doubts over US support and a bloody stalemate on the ground.

There are fears that a lack of adequate support from the West could end up forcing Kyiv to seek a compromise with Russian President Vladimir Putin from a position of weakness.

"We just have to stay the course. This is also about our security interests," NATO Secretary General Jens Stoltenberg said at a meeting of the alliance's foreign ministers in Brussels.

US Secretary of State Antony Blinken said the NATO talks were aimed at "strongly reaffirming our support for Ukraine as it continues to face Russia's war of aggression".

The United States has provided more than $40 billion in security aid to Ukraine since Russia's invasion and pledged to back Kyiv for as long as necessary.

But opposition from hardline Republicans has thrown into question the future of US assistance.

Stoltenberg said he was "confident" the United States would keep on arming Ukraine.

"It is in the security interest of the United States to do so and it's also in line with what we have agreed," Stoltenberg said.

Stoltenberg pointed to recent pledges from Germany and the Netherlands worth 10 billion euros ($11 billion) as proof that the alliance remained committed to backing Kyiv.

"Even though the frontline has not moved so much, the Ukrainians have been able to inflict heavy losses on the Russian forces," he said.

Concerns have ratcheted up over the future of Western backing for Ukraine as Kyiv's top general has admitted that the fierce fighting has reached a "stalemate".

The European Union is currently also struggling to agree a plan for its own long-term support for arming Ukraine in the face of opposition from Hungary.

Ukrainian Foreign Minister Dmytro Kuleba said in Brussels that he does "not feel any pressure" from Ukraine's backers to begin negotiations with Russia.

Germany's Foreign Minister Annalena Baerbock said the necessity of supporting Ukraine was "not about whether Ukraine can still make any progress militarily, it's about saving people".

- 'Good strategy' -

Her French counterpart Catherine Colonna said that Kyiv was facing some of the heaviest air attacks since the start of the war.

"We are underscoring out support for Ukraine which must obviously last for the long-term," she said.

Latvian top diplomat Krisjanis Karins said Ukraine needs more "long-range missiles so that they can impede Russia's logistic capabilities".

Canada's Foreign Minister Melanie Joly pushed back against suggestions that Ukraine needs to change its strategy as the war drags towards a third year.

"We have a good strategy and Ukraine has a good strategy, but we need to implement it," she said.

Kuleba and his NATO counterparts on Wednesday are set to agree on a plan for reforms aimed at helping Ukraine towards eventual membership in the alliance.

Ukraine is pushing to join NATO, but the US-led alliance has so far refused to issue a formal invitation despite promising that Kyiv will be in its ranks one day.