WASHINGTON: President Barack Obama and his Afghan counterpart Hamid Karzai vowed on Wednesday to prevent a flare-up of anti-American violence in Afghanistan after the killing of US diplomats in Libya.

Flags were lowered at US installations around the world, and Obama ordered increased security at American diplomatic missions following Tuesday's deadly assault in the eastern Libyan city of Benghazi on the 11th anniversary of the September 11 attacks.

The assault, which killed Washington's ambassador to Libya and three colleagues, was triggered by a mob angered by a film deemed offensive to Islam that Afghanistan has condemned as “inhuman and insulting.”

During their telephone call, Obama and Karzai “discussed the importance of working together to help ensure that the circumstances that led to the violence in Libya and Egypt do not pose a threat to US forces or Afghans,” the White House said in a statement.

Thousands of Egyptian demonstrators tore down the Stars and Stripes at the US embassy in Cairo on Tuesday and replaced it with a black Islamic flag similar to one adopted by several militant groups.

The White House said Karzai expressed condolences for the “tragic” deaths in Libya during the call.

The crudely produced low-budget movie, whose director goes by the name Sam Bacile and is believed to be Israeli American, pokes fun at the Prophet Mohammed, showing him sleeping with women and touching on themes of pedophilia and homosexuality.

The film has been promoted by controversial US pastor Terry Jones, who has drawn protests for burning the Koran and vehemently opposing the construction of a mosque near Ground Zero in New York.

Karzai and Obama's conversation was billed as part of regular consultations ahead of a security transition to Afghan responsibility in the war-wracked country by the end of 2014, when US forces are set to withdraw after more than a decade.

Obama also “reaffirmed his commitment to transferring detainees to Afghan authority in a manner that respects Afghan sovereignty and protects US and Afghan forces,” the statement said.

The two leaders were set to speak again soon.

Insults to Islam are taken very seriously in deeply conservative Afghanistan, where the Taliban are fighting a 10-year insurgency against 117,000 Nato troops and the US-backed government.

Riots killed around 40 people earlier this year after US troops burnt copies of the Quran on a military base.