Speaking after a NATO summit that saw the alliance also agree to take in Finland and Sweden, Biden said the United States and its NATO allies were united in standing up to Russian President Vladimir Putin.

"I don't know how it's going to end, but it will not end with Russia defeating in Ukraine," Biden told a news conference. "Ukraine has already dealt a severe blow to Russia."

Biden, who appeared to be readying allies for a long conflict in Ukraine despite talk in March of a possible victory, added: "We are going to support Ukraine for as long as it takes." He declined to give more details.

The pending formal announcement of more weapons would comes on top of the more than $6.1 billion already announced by the United States since Russia forces rolled into Ukraine on Feb. 24 and brought full-scale war back to Europe.

The plans for fresh aid, as NATO repositions itself again on a Cold War footing with a massive forces build-up, came as Ukrainians used Howitzers to retake Snake Island.

Biden had earlier pledged more American troops, warplanes and warships for Europe as NATO agreed to strengthen its deterrents, putting more than 300,000 troops on high alert from the middle of next year.

"The U.S. is doing exactly what I said we would do if Russia invaded, enhance our force posture in Europe," Biden said. "The United States is rallying the world to stand with Ukraine."

RUSSIAN REPRISALS?

British Prime Minister Boris Johnson said London would provide another 1 billion pounds ($1.22 billion) in military aid to Ukraine, while his French counterpart Emmanuel Macron said France would soon deliver six more CAESAR guns.

Britain's contribution includes air defence systems and new electronic warfare equipment, taking support to more than 2.3 billion pounds since Moscow's invasion, a financial sum the British government said was second only to U.S. aid.

Putin did not appear ready to withdraw or negotiate the terms of a peace deal, Johnson said.

"There doesn't seem to be anything to talk about. Because it's not only that the Ukrainian people would find it very difficult to do a deal, Putin isn't even offering a deal," Johnson told a news conference.

In the biggest shift in European security in decades, Finland and Sweden will sign the formal accession protocol next Tuesday to join NATO, NATO Secretary-General Jens Stoltenberg said, although ratification could take a year.

Putin said on Wednesday that Russia would respond in kind if NATO deployed troops or infrastructure in Finland or Sweden, whose decision to join NATO was prompted by Moscow's decision to wage war in Ukraine. The Kremlin calls it a "special operation".

Estonian Prime Minister Kaja Kallas said the West needed to be ready, particularly in terms of possible attacks on Finnish, Sweden and NATO computer networks. "Of course, we have to expect some kind of surprises from Putin, but I doubt that he is attacking Sweden or Finland directly," she said.

Lithuanian president Gitanas Nauseda added: "This is the style of this (Russian) regime, to try to scare us."

FIGHTING ON ALL FLANKS

While the three-day summit was dominated by NATO's response to Russia's war in Ukraine, host Spain urged allies to consider a bigger role for the alliance in North Africa and the Sahel.

NATO was created in 1949 to defend against the Soviet Union.

Western powers are concerned about a spike in violence in Mali, where the country's ruling military junta, backed by Russian private military contractor Wagner Group, is battling an Islamist insurgency that spills into neighbouring countries in the African region known as the Sahel.

France, whose military policy has long been focused on NATO's south, said in February that it would pull out 2,400 troops, after relations with the junta turned sour.

At Spain's urging, with support from Italy, NATO's new, 10-year master document, the "strategic concept" cites terrorism and migration as elements to monitor, and points to the southern flank as a new source of risk to stability.

Britain's Johnson said he would support a bigger NATO role in the Sahel, although he did not go into details.

Spanish Foreign Minister Jose Manuel Albares said the region "is the epicentre of global terrorism".

"If the threat were very present and very concrete, we could see a reinforcement of military deployment on the southern border as we are seeing in the east," he said.

($1 = 0.8228 pounds)

(Additional reporting by Sabine Siebold, Humeyra Pamuk, Belen Carreno, Aislinn Laing, Andrea Shalal in Madrid, Alan Charlish in Warsaw and William James in London; Writing by Robin Emmott; Editing by Alison Williams)

By Andrea Shalal, Aislinn Laing and Robin Emmott