At least twelve people are dead and several more have been injured in twin shooting and suicide bomb attacks at the Iranian parliament and the the Mausoleum of Ayatollah Khomeini in Tehran, said media reports.

Gunmen went on a shooting spree in the parliament, where at least one attacker detonated a suicide bomb. At the same time, a gun and bomb attack targeted the Ayatollah Khomeini mausoleum on the southern outskirts of the Iranian capital, reported CNN.

One guard and six others were killed in the incident in parliament early on Wednesday, Tasnim news agency reported.

The Iranian Intelligence Ministry said security forces had arrested a "terrorist team" planning a third attack, without giving further details. The head of Iran's emergency department, Pir-Hossein Kolivand, was quoted as saying by state broadcaster IRIB that 39 people were wounded in the attacks.

Islamic State claimed responsibility for the attacks in a statement.

Earlier in the day, reports emerged that a suicide bomb was detonated on the fourth floor of parliament and several people had been taken hostage later on Wednesday morning.

In the mausoleum attack assailants killed a security guard and injured at least four others at the mausoleum in southern Tehran, state television said.

A woman was arrested after the attack at the tomb, according to the semi-official Fars news agency. As per the agency's reports another attacker has been surrounded by security officers. Two people were injured there.

The attackers were holding a number of hostages inside the highly-fortified parliament building, Press TV reported, as Iranian officials scrambled to establish who was behind the attacks or whether they were coordinated.

A witness told Reuters the parliament's entrances were barricaded as security forces massed inside and outside. There are conflicting reports as to how many gunmen were involved but at least four people have been taken hostage.

Unconfirmed reports said that the attackers had been looking for the chamber where MPs were in session, but lost their way once inside the building.

At least one male assailant escaped the building but was captured as he was on the run, the agency reported.