KYIV, Ukraine (AP) – The U.S. has issued some of its starkest, most detailed warnings yet about how a Russian invasion of Ukraine might unfold. Its Western allies are on high alert for any attempts by the Kremlin to create a false pretext for a new war in Europe. U.S. President Joe Biden sounded unusually dire Thursday. He warned that Washington saw no signs of a promised Russian withdrawal – but instead saw more troops moving toward the border with Ukraine. He said Moscow could invade within days. Western fears focus on an estimated 150,000 Russian troops posted around Ukraine’s borders. The Kremlin insists it has no plans to invade, but it has long considered Ukraine part of its sphere of influence.