TEHERAN - Gunmen and suicide bombers stormed Iran's parliament and the shrine of its revolutionary leader on Wednesday, killing 12 people in the first attacks in the country claimed by the Islamic State group.

Dozens of people were wounded in the attacks, which ended after a standoff lasting several hours as the gunmen holed up in parliamentary office buildings.

IS released a video of the attackers from inside the building via its Amaq propaganda agency - a rare claim of responsibility while an attack was still going on.

Police said all the attackers had been killed by around 3 pm, five hours after it started.

The assaults began in the morning when four gunmen burst into the parliament complex in the center of Teheran, killing a security guard and one other person, according to the ISNA news agency.

An Interior Ministry official said they were dressed as women and entered through the visitors' entrance.

At roughly the same time, a team of three or four assailants entered the grounds of the mausoleum of Ayatollah Ruhollah Khomeini, who led the 1979 Islamic Revolution, killing a gardener and wounding several other people.

Iran's emergency services said a total of 12 people were killed and 42 wounded.

Two of the attackers at the shrine, one of them a woman, blew themselves up, while another detonated a suicide vest on the fourth floor of the parliamentary office building.

A picture on social media showed police helping staff escape through windows.

Large crowds gathered around cordons to watch as police dispersed the crowds.

Parliament was in session as the attacks unfolded and members were keen to show they were undeterred, continuing with regular business.

Some posted selfies of themselves looking calm, even as gunbattles raged in surrounding buildings and snipers took position on nearby rooftops.

An official at Khomeini's mausoleum said "three or four" people had entered via the western entrance and opened fire, according to the Fars news agency. It published photos showing the suicide bomber blowing herself up outside.

The Intelligence Ministry said there had been a third terrorist team that was neutralized before the attacks started.

The city was on lockdown, with streets blocked and parts of the metro closed.

Increasing pressure

The Sunni extremists of IS consider Shiite Iran to be apostates, and Teheran has been helping both Iraq and Syria to battle the group.

IS is under increasing pressure in both countries, having lost significant territory in the face of offensives now targeting its last two major bastions, Raqa in Syria and Mosul in Iraq.

The group published a rare video in Persian in March, warning that it "will conquer Iran and restore it to the Sunni Muslim nation as it was before".

Iran's supreme leader Ayatollah Ali Khamenei said on Sunday that attacks by IS in Europe and elsewhere showed that Western policies in the Middle East have backfired.

"This is a fire that they ignited and now has backfired on them," he told a gathering of senior officials in Teheran.

Afp - Ap