ANKARA (Reuters) – Iran said on Thursday that gunmen and bombers who attacked Tehran were Iranian members of Islamic State who had fought in the militants’ strongholds in Syria and Iraq – deepening the regional ramifications of the assaults.

The attackers raided Iran’s parliament and Ayatollah Khomeini’s mausoleum on Wednesday morning, in a rare strike at the heart of the Islamic Republic. Authorities said the death count had risen to 17 and scores were wounded.

Iran’s powerful Revolutionary Guards have also said regional rival Saudi Arabia was involved, further fuelling tensions between Sunni Muslim power Riyadh and Shi’ite power Tehran as they vie for influence in the Gulf. Saudi Arabia dismissed the accusation.

Iran’s intelligence ministry said on Thursday five of the attackers who died in the assault had been identified as Iranians who had joined the hardline Sunni Muslim militants of Islamic State on its main battlegrounds in Iraq and Syria.

“They earlier left Iran and were involved in the crimes of the terrorist group in Raqqa and Mosul,” the ministry said, referring to Islamic State’s effective capital in Syria and a city it captured in Iraq.

“Last year, they returned to Iran … to carry out terrorist attacks in the holy cities of Iran,” the ministry added in a statement on state news agency IRNA.

The attacks were the first claimed by Islamic State inside the tightly controlled country, one of the powers leading the fight against the militants in neighboring Iraq and beyond that Syria.

Islamic State claimed responsibility and threatened more attacks against Iran’s majority Shi’ite population, seen by the hardline Sunni militants as heretics.

Iran’s intelligence ministry said earlier on Thursday it had arrested more suspects linked to the attacks, on top of six Iranians, including one woman, detained on Wednesday.

Militant attacks are rare in Tehran and other major cities although two Sunni militant groups, Jaish al-Adl and Jundallah, have been waging a deadly insurgency, mostly in remote areas, for almost a decade.

(Writing by Parisa Hafezi; Editing by Andrew Heavens)