Qatar's foreign ministry condemned twin attacks that killed 12 people in Iran on Wednesday, according to a statement on its website.

Doha -- which is under intense pressure from other Gulf countries who accuse Qatar of supporting Iran and Islamist groups -- said it also took a "firm stance" against violence and rejected criminal acts.

"The State of Qatar has condemned and denounced the two attacks which took place in Iranian capital Tehran and left many people killed and injured," read the statement.

Qatar also expressed its condolences "to the government and people of Iran".

Twelve people were killed when gunmen and suicide bombers stormed Iran's parliament and the shrine of its revolutionary leader.

The assaults were claimed by the Islamic State group, the first time it has taken responsibility for an attack in Iran.

Qatar has denied support for Iran and extremists during a diplomatic crisis which has seen Saudi Arabia and its allies cut ties with Doha and put it under intense pressure to bring its foreign policy in line with other states in the Gulf.