The fighting in Jazan, on the frontier with Yemen, is not some little local border dispute: Relations with Yemen are excellent. Nor it is the result of a border drawn arbitrarily across the traditional lands of some tribe that resents the division and rejects the power of the authorities on both sides of it. This was a coordinated attack on Saudi Arabia’s integrity and sovereignty. The Al-Houthi Yemeni rebels attempted to seize territory in the country and in the process brought violence and death to the area. Saudi Arabia’s first duty is to protect its citizens and defend its territory. The Yemeni rebels can rest assured it will do so. They will be crushed as decisively as would be any attackers who try elsewhere in the Kingdom, whether Riyadh, Dammam or even Makkah.

The question, however, is why did these Yemeni rebels attack? They were not chased across by Yemeni forces whom they have been fighting since August following their abrupt termination of last year’s cease-fire with the government in Sanaa. The attack on the border posts and attempted seizure of Saudi villages was a deliberate and planned act of aggression. The aim was to hurt and embarrass the Kingdom. So who was behind it?

It is impossible not to see the hand of Iran in this. They have been supporting the Houthi rebels, who like them are Shiites, with arms and money. Only last week, Yemen announced that it had intercepted a vessel carrying Iranian weapons for the rebels.

Saudi Arabia has always tried to extend its hand in friendship toward Iran. It has supported its right to develop the technology for nuclear energy. It has been opposed to American attempts to demonize the country and ratchet up the tension with it. It has never tried to interfere in its internal affairs, even if there is plenty to complain about, not least its institutional oppression of its Arab citizens. Saudi Arabia has, moreover, always believed that dialogue is the best means of resolving any differences with Tehran.

But there are red lines that cannot be crossed. Interference in the Kingdom by any foreign power will not be tolerated. Not just in Kingdom. Interference in Iraq, in Lebanon, in Yemen — anywhere in the Arab world — is wholly unacceptable. We loudly oppose American interference and Israeli interference in Arab affairs. Are we going to keep quiet if it is Iran that is interfering?

In recent weeks, the accusation that Iran wants to establish a hegemony over the Arabs, with Shiite states in Iraq, Lebanon, north Yemen and the western side of the Gulf, becomes more difficult to ignore. Officials in Iran have been deliberately provocative, ratcheting up the temperature. There have been false allegations that Iranian pilgrims during Haj would be mistreated. This attempt to politicize the Haj deeply offends. There has been the constant drip of Iranian interference in Lebanon and Iraq. And now there is Yemen and Jazan.

Iran has few friends as it is. Saudi Arabia and other GCC countries want to be good neighbors. Stability and security for all — including Iran — is the goal. But Tehran’s policies are radically and rapidly changing the political climate in the region.