hanoi vietnam prime minister urge great u.s. role prevent militarization island-building south china sea government say tuesday rare call washington support curb beijing maritime expansionism summit southeast asian countries california monday premier nguyen tan dung suggest u.s. president barack obama washington use strong voice practical efficient action comment likely rile china tension spike since beijing construction seven islands spratly archipelago prime minister dung suggest unite state strong voice practical efficient action request termination activities change status quo government say news website statement specifically name china say dung refer especially large-scale construction artificial islands militarization large u-shaped line official map china claim south china sea malaysia philippines taiwan brunei vietnam rival claim obama ally southeast asia turn attention china tuesday second day summit intend improve trade provide unite front maritime dispute beijing whereas china accuse unite state seek maritime hegemony asia washington say interest south china sea preserve freedom navigation recent months unite state raise stake send guided-missile destroyers uss lassen uss curtis wilbur close dispute areas occupy beijing though communist vietnam routinely oppose china activities dispute water leaders usually wary provoke giant neighbor share 60 billion annual trade maintain close ideological tie dung earn popularity vietnam pursue strong u.s. trade defense link take tough line china compare measure responses vietnamese leaders beijing assertiveness dung controversially overlook politburo last month nomination party chief mean end political career term end year pose possible blow washington dung also ask obama fully lift lethal arm embargo vietnam would important way strengthen political trust government website quote say obama visit vietnam may white house say vietnam pm want strong u.s. role south china sea