yangon members u.s. congress say tuesday disturb harsh response myanmar security force attack militants august say bore hallmarks ethnic cleanse rohingya muslim minority profoundly disturb violent disproportionate response rohingya military local group democratic senator jeff merkley tell reporters yangon end visit bangladesh myanmar merkley member senate foreign relations committee lead five-strong congressional delegation last days meet people affect military crackdown rohingya muslims force 600,000 people flee bangladesh early november u.s. lawmakers propose target sanction travel restrictions myanmar military officials treatment rohingya myanmar operation rohingya 'hallmarks ethnic cleanse u.s. congress members say