(CNN) -- European Union leaders threatened sanctions against the Ivory Coast and said members of the country's military should support Alassan Ouatarra, who international officials say won the presidency.
The European Council called on Ivorian troops "who have not yet done so, to place themselves under the authority of the democratically elected president" in a statement issued Friday after a meeting in Brussels, Belgium,
The leaders also reiterated an earlier pledge to take "targeted restrictive measures" against the Ivory Coast, including freezing assets and banning visas.
It was the latest in a chorus of international criticism of incumbent President Laurent Gbagbo, who claims to have won the election.
The Ivory Coast's Independent Electoral Commission said Ouattara won the November 28 presidential runoff, but the country's Constitutional Council invalidated those results and declared Gbagbo the winner. The United Nations, the Economic Community of West African States, the European Union and the African Union said Ouattara won.
"Laurent Gbagbo and his spouse have their own fate in their hands. If by the end of the week, Laurent Gbagbo will not leave the position he occupies in violation of the will of the Ivorian people, their names will specifically be put on the list of sanctions," French President Nicolas Sarkozy said during the European leaders' meeting Friday.
U.S. State Department spokesman P.J. Crowley said Friday that the U.S. was also prepared to impose sanctions on "Gbagbo, his immediate family and his inner circle, should he continue to illegitimately cling to power."
Violence has broken out between supporters of Gbagbo and Ouattara.
U.N. Secretary-General Ban Ki-moon said Friday that Gbagbo's efforts to maintain his office "cannot be allowed to stand."
Ban called Friday for Gbagbo to step down and said that "any other outcome would make a mockery of democracy."
"The results of the election are known. There was a clear winner. There is no other option," Ban said.
Since November's runoff elections, there has been a political stalemate.
At least nine unarmed protesters in Abidjan, Ivory Coast's largest city, were shot and killed by security forces during protests Thursday, witnesses told Amnesty International. The violence erupted as troops loyal to the incumbent president and supporters of his challenger confronted each other.
Saying the "situation has taken a dangerous turn," Ban urged both sides "to avoid provocations or a further escalation of violence."
CNN's Mila Sanina contributed to this report.