"The United States calls for an immediate end to the violence," Clinton said in a statement that took aim at Gbagbo, who is resisting calls from the world community to hand the presidency to recognized November election winner Alassane Ouattara.

She said the "United States strongly condemns" attacks by Gbagbo's forces on his own people, including one Thursday on unarmed women demonstrators that left seven dead. His forces denied responsibility.

"Gbagbo and his forces have shown a callous disregard for human life and the rule of law, preying on the unarmed and the innocent. He should step aside immediately in the name of peace," she said.

"Gbabgo's selfish effort to cling to power despite losing the election has elevated tensions and eroded the fundamental rights of Ivoirian civilians," the chief US diplomat said.

"Since December, Gbagbo has used security forces to attack the very people he claims to represent, and deprived Ivorian citizens of access to water and electricity," said the secretary.

In calling for an end to the violence, she said: "Military leaders, regime officials, and others responsible for directing or committing violent acts against civilians will have to answer for their actions."