washington u.s. state department say sunday watch developments dispute region kirkuk concern report confrontation iraqi government force clash kurdish peshmerga monitor situation kirkuk closely concern report confrontation state department official say engage party iraq de-escalate tension iraqi government early say force take control vast areas kirkuk region include oilfields west city early hours monday iraqi state tv say however kurdistan regional government dispute assertions u.s. state department say 'very concern report kirkuk confrontation