U.S. Ambassador Samantha Power is warning that "horrible attacks" on both sides in Burundi risk creating "a cycle of violence and a spiral of violence."

The capital Bujumbura has been hit by violence since April when the ruling party announced that President Pierre Nkurunziza would seek re-election for a third term. Nkurunziza was re-elected last month in elections that were widely condemned as unfair.

Power urged the government and opposition on Friday to participate in internationally mediated talks and come up with political arrangements "that will calm tempers, allow civil society and independent media to be reconstituted."

She said the United States and many other countries are looking at possible visa or travel bans and other sanctions against those responsible for gross violations of human rights or "murderous attacks."