Human Rights Watch says the rise of the Islamic State group is among the world's top challenges and blames "sectarian and abusive" policies of the Iraqi and Syrian governments for fueling extremism.

In its annual report, the New York-based group accuses the U.S. and its allies of allowing military action against the IS to overshadow efforts to push Syrian President Bashar Assad's government to end its own abuses.

It also accuses the Iraqi government of relying in the battle against IS primarily on Shiite militias who are killing and cleansing Iraqi areas of Sunni civilians with impunity.

HRW also accuses the international community of indifference to the violations by both governments.

The 656-page World Report 2015 was released in Beirut Thursday, reviewing human rights practices in more than 90 countries.