By Michelle Nichols and Humeyra Pamuk UNITED NATIONS (Reuters) -U.S. Secretary of State Antony Blinken laid out at the United Nations Security Council on Thursday how Washington believes Russia could seek to invade Ukraine, warning that Moscow was preparing to attack its neighbor in the “coming days.” Blinken, as other U.S. officials have done over the past two weeks, accused Russia of planning to manufacture a pretext for an attack on Ukraine that could include “a fake, even a real, attack using chemical weapons,” and said: “Russia may describe this event as ethnic cleansing or a genocide.” R…