Coffin of one of dead is transported after gunmen killed 21 people including many high school students after dragging passengers off buses in the town of Ain Laila

Iraqi police say insurgents killed at least 36 people Sunday as political leaders again fail to agree on candidates for two key ministries.

Police say gunmen killed 21 people, mostly students, after dragging them off buses at a makeshift checkpoint north of Baghdad.

A man wounded in the attack told VOA Kurdish Service from Sulaimaniya hospital the gunmen asked the passengers if they were Sunni Arab, Shi'ite, Kurdish, or Turkmen. The four Sunnis were spared and are being questioned by Iraqi authorities.

Elsewhere, Iraq's Interior Ministry says gunmen killed four employees of a telephone company near Baghdad's Sadr City. And police say 11 people were killed in a clash at a Sunni mosque in Basra.

In other developments, U.S. Secretary of State Condoleezza Rice downplayed delays in selecting Iraqi defense and interior ministers. She says she believes those major posts will be filled in the coming days.

Rice also told CBS television Sunday that November's alleged massacre of Iraqi civilians by U.S. Marines in the town of Haditha will be fully investigated.

She said all accused are innocent until proven guilty and that the majority of U.S. soldiers in Iraq are taking casualties and making sacrifices to protect the Iraqi people.

U.S. Marines allegedly shot and killed 24 Iraqi civilians in Haditha after a bomb blast killed a fellow Marine. Some U.S. lawmakers believe Marine officers tried to cover up the incident.