BEIRUT • Iran's Islamic Revolutionary Guard Corps (IRGC) was quick to condemn the execution of Saudi cleric Sheikh Nimr al-Nimr, stating: "Without a doubt, the hated Saudi regime will pay a price for this shameful act."
For an organisation deeply involved in wars in Syria and Iraq, this looks no idle threat - at least in the eyes of Sunni Gulf Arab states such as Saudi Arabia who say Shi'ite rival Teheran is bent on undermining their security.
The IRGC's furious comment is not a call for direct conflict with Riyadh, something neither country wants.
But it is a reminder to Gulf Arabs that the IRGC, with connections in Saudi Arabia and elsewhere in the region, has many ways to wage the long cold war between Iran and its Arab foes.
Bahrain said yesterday it had uncovered an Iranian-linked cell plotting attacks in the Gulf island kingdom, Saudi-owned Al Arabiya TV reported.
"Bahrain (announces) the apprehension of a terrorist cell linked to the Revolutionary Guard and Hizbollah... the members of the cell plotted bombings in the country," Al Arabiya said.
Teheran has always denied interfering in Arab lands.
But the Quds Force, the arm of the IRGC that operates abroad, has contributed fighters, weapons and military supplies to back Iran's interests and policies across the region.
That prospect is worrying for a region where conflicts or political crises from Lebanon and Syria to Yemen, Iraq and Bahrain involve proxies of both powers who are at daggers drawn.
A day after the IRGC issued its statement, which described Saudi rulers as "terrorist-fostering, hated and anti-Islam", Riyadh broke off diplomatic relations with Teheran, escalating a contest for power that underpins the region's turmoil.
There is no firm indication that Iran's factionalised leadership has agreed on how far it should go to avenge the death of Sheikh Nimr - who was one of 47 people executed by Saudi Arabia on Saturday - and what methods should be used.
"They have their operatives, their people, their connections everywhere in the region who will answer what the Saudis did and actually escalate (matters)," said professor of political science Hilal Khashan at the American University of Beirut.
Moderate voices on both sides do not have an interest in seeing the situation escalate into a full conflict, experts say.
And yet the rivals often compete indirectly through allies, which lends the contest an element of unpredictability: Some Iranian proxies may be encouraged by the tough rhetoric coming from Teheran to carry out attacks not sanctioned by the IRGC.
"Both sides are loath to see tensions spiral out of control," said International Crisis Group senior Iran analyst Ali Vaez.
"But with tensions reaching new heights, now more than ever, they run the risk of unintended direct confrontation."