A U.S. government website has published what it says is photographic evidence of mass graves and attacks on civilian areas by Syrian government forces.

A website operated by the State Department — humanrights.gov — published the satellite images Friday.

More than 100 people, nearly half of them children, were killed in a massacre in Houla on May 25. The killing has sparked widespread outrage, with some leading diplomats calling for an international coalition to remove Syrian President Bashar al-Assad from power.

The U.S. ambassador to Syria, Robert Ford, says Syria's assault on Houla is “the most unambiguous indictment” of the Syrian regime to date.

The United Nations human rights chief has called for an independent investigation into the killings in Houla. Navi Pillay said the Syrian government should provide full access to investigators to look into what could be crimes against humanity.

On Friday, Syrian activists reported the killing of at least 12 more civilians.