The United States will provide urgently needed assistance to Iraq's security forces, but Iraqis must pull together to fight the "vicious" insurgency that threatens to break up the country, U.S. Vice President Joe Biden said on Tuesday.

"Urgent assistance is clearly required," said Biden during a visit to Brazil. "The bottom line here is that Iraqis have to pull together to defeat this enemy."

Biden said this would require setting aside sectarianism, building an inclusive security force and ensuring that all communities in Iraq have their voices heard.

The opportunity to do this exists now after the Iraqi Supreme Court certified the election results on Monday, he said in a statement to reporters after visiting Brazil's president.

Washington has made clear it wants Iraqi Prime Minister Nuri al-Maliki to embrace Sunni politicians as a condition of U.S. support to fight a lightning advance by forces from the Islamic State of Iraq and the Levant.