By Idrees Ali and Sabine Siebold
BRUSSELS (Reuters) -Russia's invasion of Ukraine was at a "pivotal" moment and the United States and its allies could not lose focus on the three-month long conflict, U.S. Defense Secretary Lloyd Austin said on Wednesday as Western countries pledged more weapons to Kyiv.
Austin was speaking at a meeting of dozens of defence ministers on the sidelines of a NATO ministerial gathering. It is the third time the group of nearly 50 countries have met to discuss and coordinate assistance to Ukraine. The previous in-person meeting was at Ramstein Air Base in Germany in April.
Ukraine needs 1,000 howitzers, 500 tanks and 1,000 drones among other heavy weapons, presidential adviser Mykhailo Podolyak said on Monday. Western countries have promised NATO-standard weapons, including advanced U.S. rockets.
But deploying them is taking time, and Ukraine will require consistent Western support to transition to new supplies and systems as stocks dwindle of their Soviet-era weapons and munitions.
"We can't afford to let up and we can't lose steam. The stakes are too high," Austin said at the start of the meeting in Brussels. "Ukraine is facing a pivotal moment on the battlefield... Russia is using its long-range fires to try to overwhelm Ukrainian positions."
The White House announced around $1 billion worth of new weapons for Ukraine on Wednesday, including coastal defence systems and ammunition for artillery and advanced rocket systems.
Germany will supply three MARS II multiple rocket launchers to Ukraine, Defence Minister Christine Lambrecht said, adding that the training of Ukrainian troops would begin in the coming weeks.
Before the start of the meeting, NATO Secretary General Jens Stoltenberg said the allies would continue to supply Ukraine with heavy weapons and long-range systems and that he expected them to agree a new package of assistance to Kyiv at a NATO summit later this month.
"Sometimes these efforts take time. That's exactly why it is important to have a meeting like we have today... to meet with the Ukrainian representatives to identify the challenges and the issues they would like to raise with us when," Stoltenberg said.
'GRINDING' OPERATION
The battle for Sievierodonetsk - a city of barely more than 100,000 people before the war - is now the biggest fight in Ukraine as the conflict has shifted into a punishing war of attrition.
Chairman of the U.S. Joint Chiefs of Staff General Mark Milley told reporters that about three-quarters of Sievierodonetsk was under Russian control.
It was not an inevitability that Russia would take over the eastern Donbas region, but it was clear the numbers favoured Russia in terms of artillery, even though Moscow had lost 20% to 30% of its armoured force, Milley told a news conference after the meeting.
The United States has committed about $5.6 billion in security assistance to Ukraine since Russia's Feb. 24 invasion, including artillery systems such as howitzers and longer-range weapons like the High Mobility Artillery Rocket System (HIMARS).
"Russia has not given up on the fight, despite its pretty anaemic progress... What we have is this grinding, slow, incremental Russian operation," said a senior U.S. defence official, speaking on the condition of anonymity.
"So the question is what do the Ukrainians need to continue the success they've already seen in slowing down and thwarting that Russian objective and that'll be a major focus for the defence ministers," the official said.
Russia launched what it calls a "special operation" in Ukraine in February, saying it was needed to rid the country of dangerous nationalists and degrade Ukraine's military capabilities - aims the West denounced as a baseless pretext.
The Biden administration has said it has received assurances from Kyiv that those longer-range weapons would not be used to attack Russian territory, fearing an escalation of the conflict.
Kyiv has said it was losing 100 to 200 soldiers each day, with hundreds more wounded. In an overnight address, President Volodymyr Zelenskiy described the battle for the Donbas industrial heartland - partly occupied by Moscow's proxies since 2014 - as one of the most brutal in European history.
Milley said those numbers were within the ballpark of the United States' estimate of Ukrainian casualties, but the losses could be sustainable since Russia's invasion posed an existential threat.