san francisco vietnamese government restrict access facebook inc inside vietnam several days week part broad crackdown human right political dissidents visit president barack obama two activist organizations say thursday officials access digital right organization viet tan vietnamese pro-democracy group say social media site restrict time block inside vietnam sunday wednesday cite report people inside country twitter access digital security help service move coincide trend toward restrictions facebook countries include china uganda turkey politically sensitive time 1.6 billion-person social network grow powerful obama three-day visit vietnam end wednesday obama largely focus normalize relations vietnam also promote human right chide vietnam restrictions political freedoms critics communist-run government prevent meet facebook shutdown part stepped-up campaign vietnamese government limit use social network political protest activists say phone interview facebook block several time early month street protest erupt environmental disaster result mass fish deaths two group say social media site also unavailable inside vietnam ahead parliamentary elections sunday pro-democracy activists call boycott members two group say facebook decline comment vietnamese government officials immediately respond request comment submit via government website uganda government block facebook twitter inc february presidential elections march deadly bomb turkey ankara court order ban access facebook twitter 2011 arab spring egypt tunisia libya social network repeatedly shut facebook often shut vietnam politically sensitive time angelina huynh advocacy director viet tan members around world include vietnam say phone interview people use facebook call protest want people take streets huynh say vietnam restrict access facebook obama visit activists