Iran’s Revolutionary Guard has blamed Saudi Arabia for two deadly attacks in Tehran carried out by Islamic State (Isil) fighters, a move that threatened to escalate the terrorists’ actions into a regional confrontation between Sunni and Shia powers.

Gunmen and suicide bombers from Isil killed 12 people when they assaulted the Iranian parliament and a symbolic shrine to Ayatollah Khomeini, the leader of the Iranian revolution, on Wednesday morning in their first major attack against Iran.

In a statement released hours after the attacks, the Revolutionary Guard said it held Saudi Arabia responsible for the Sunni jihadist group’s actions and promised revenge. Iranian commanders pointed the recent summit between Donald Trump and Gulf Arab leaders, where Saudi Arabia called for a harder line against Iran.

“This terrorist attack happened only a week after the meeting between the US president and the backward [Saudi] leaders who support terrorists. The fact that Islamic State has claimed responsibility proves that they were involved in the brutal attack,” the Revolutionary Guard said.