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…