ISIS claimed responsibility for the bombing, but they claim lots of attacks.
Gunmen, some reportedly dressed as women, but also wearing suicide vests, attacked the Tehran parliament building with guns. A standoff with police lasted hours.
6 attackers were killed, 5 arrested.
If ISIS was indeed responsible, it would be the first time their Sunni extremist group has successfully attacked Shia Iran, although they have been trying, reportedly. It is difficult for Sunni extremists to attack Iran because Iran is around 90% Shia, and Tehran is around 95% Shia, so there is not much of a reservoir of support for themthere.
ISIS would see an attack on Iran as a huge symbolic victory, according to analysts, as ISIS is against Iran like it's against the U.S.
Iran blamed Saudi Arabia for the attack and vowed retaliation. The longstanding conflict between Middle East countries continues.