The Islamic State, a Sunni jihadi group, claimed responsibility for both attacks in the Shia majority nation. Shops in the area were shuttered, and gunfire could be heard. Islamic State has regularly threatened Iran, one of the powers leading the fight against the militants' forces in neighbouring Iraq and, beyond that, Syria. The semi-official Tasnim news agency later reported the siege had ended with four of the attackers killed.
Jaish al-Adl (or the Army of Justice) is a Sunni militant group that has carried out several attacks on Iranian security forces mainly in Sistan-Baluchestan. There, four attackers, including a suicide bomber, killed a security guard and wounded four other people.
The violence unfolded at about 10 a.m. local time (2 a.m. ET) when gunmen apparently dressed as women stormed the main gate of the parliament building in central Tehran and opened fire, Iran's Deputy Interior Minister Mohammad Hossein Zolfaghari told state television.
Khomeini was Iran's first Supreme Leader and he led the 1979 uprising that toppled the last shah of Iran.
The attackers took a number of hostages and at least one detonated a suicide bomb.
In an unusual development, the group also released a short video that it said was taken by one of the attackers inside the parliament. The Intelligence Ministry said security forces had arrested another "terrorist team" planning a third attack, without giving further details. Quoting sources on the ground, Tasnim news agency reported that seven people, including a guard, were killed. The attack interrupted an active Parliament committee session.
"It is astounding what Iran continues to do around the world", said Corker, urging his colleagues to confront the threat Tehran poses.
Iran has stepped up its crackdown against members of such networks in recent years, with mass arrests and death sentences. This is not the first time that Iran has come under attack, but the latest attack is the first time that a major urban center in Iran has been hit.
The other said the attacks, and speculation over who backed them, would push Iran toward "a harsher regional policy".
The "spilled blood of the innocent will not remain unavenged", the Revolutionary Guard statement said.
An Associated Press reporter saw several police snipers on the rooftops of buildings around parliament.
Soon after the parliament attack, a suicide bomber and other assailants targeted the mausoleum of Khomeini, located just outside the capital, Tehran, according to Iran's official state broadcaster. An estimated eight percent of Iran is Sunni Muslim, compared to 89 percent Shiite.
The parliament, the Islamic Consultative Assembly or Majlis, is Iran's principal legislative body.