As tensions escalate between Saudi Arabia and Iran over the Saudi execution of a Shia cleric, countries such as ours will be reluctant to take sides. Certainly, Western nations should not automatically side with the Saudis, who have been the more reliable ally since Iran went under religious rule. But while Iran's antagonism to the West has softened under its latest elected government, helped by United States diplomacy under President Barack Obama, Saudi Arabia appears to be fomenting more trouble in the region. Its execution of Shia political activists at the weekend - one of them prominent cleric Sheikh Nimr al-Nimr - appears to be calculated to deepen Islam's sectarian divide.

The Saudis must have expected the demonstrations against its embassy in Tehran, yet it retaliated by recalling its diplomats, expelling Iran's representatives and severing diplomatic relations. Bahrain and other Gulf states have been quick to back the Saudis, as has a Sunni majority state as far away as Sudan. Russia has been equally quick with an offer to intercede, though it is hardly in a position to do so having made itself an ally of Iran in the Syrian war. Both are supporting the Assad regime against various tribal and sectarian groups, including the Sunni "Islamic State" of Iraq and Syria.

The Saudis' attitude to Isis has never been clear. Last month, the kingdom announced it was setting up a 34-nation Islamic coalition to combat the "disease" of extremism, but nothing has been done and the initiative has been seen as little more than a claim to leadership of the region to the exclusion of Iran. The Saudis have not acted on other counter-terrorism commitments they made last year in a Jeddah Communique with the US, in which they agreed to stop the flow of finance to Isis, repudiate its ideology and help reconstruct communities destroyed by the jihadists in Syria and Iraq.

The mass execution of 47 people on Saturday - the largest carried out by the Saudi regime for 35 years - involved beheading in some cases. When Isis carried out that barbaric practice it is rightly condemned, when Saudi Arabia uses it, the world has for too long looked away. Capital punishment of any kind ought not be condoned in diplomacy. As more states of the US slowly discontinue the practice, and no other Western country kills its own citizens, states like Saudi Arabia should be confronted with civilised disapproval.

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The West has no interest in the contest between Sunni and Shia branches of Islam. It is only by staged beheadings and threats of terrorism that Isis has drawn some Western countries back into the internecine war. Saudi Arabia and Iran have been the crucial powers all along. The Saudis were not happy at Iran's deal with the US to forego nuclear weapons and would dearly like to drive a wedge through the agreement. They know conservative opinion in the US dislikes the deal too.

But the execution of a Shia leader who came to prominence in the Arab Spring five years ago is no way to win friends in the West. Iran is looking more respectable by the day.