Ribera's comments contrasted with the extremely cautious line of the European Commission, which has declined to condemn the killings and called the violence in Minneapolis an "internal" US matter.
The US-based Human Rights Activists News Agency (HRANA) said it has confirmed 6,479 people killed in the demonstrations, including 6,092 protesters and 118 children, as internet restrictions imposed on January 8 continue to hinder access to information inside the country.
The World Food Programme said it urgently needs $32 million for the next three months' operations, saying it was stepping up efforts to reach more than 450,000 people.
The extraordinary meeting that lasted four hours was called after 13 countries led by the Netherlands expressed in a letter seen by AFP a "growing concern about the severity and urgency of nuclear safety risks" following a series of attacks.