"Congress has a responsibility to deal with these issues," U.S. President Barack Obama says on a Sunday-morning talk show.
Witnesses said the 28 victims were told to lie down in the mud and then were shot to death.
The Pentagon hopes to send $24 million worth of weapons to tribesmen in Iraq to fight Islamic State militants.
It's unclear whether the U.S. and the other members of the P5+1 group can come to an agreement with Iran over its nuclear program.
The Stalinist state has reacted with anger over a U.N. vote that suggested it face crimes-against-humanity charges.
The Russian president says his country won’t be isolated as a result of economic sanctions over Ukraine.
Some families have had mothers, daughters and sisters kidnapped and sold into slavery by Islamic State group militants.