Saudi Arabia's execution of 47 prisoners for offences of terrorism and "breaking allegiance with the ruler" flies in the face of the worldwide campaign against the death penalty, in which the European Union plays the leading role.
European efforts towards conflict resolution in Syria and across the Middle East and North Africa have also suffered a huge setback, in the serious breakdown in already fractious relations between the Saudis and Iran which has resulted.
The first priority for the EU must be renewed efforts to ensure that the close ties that exist between European countries and Saudi Arabia are used to promote genuine respect for human rights.
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My own country, the UK, has failed to properly criticise Saudi Arabia for its actions, calling the executions merely "disappointing". The British government has excluded Saudi Arabia in its strategy document identifying 65 countries with whom to lobby against continued use of the death penalty.
I back calls by my national MP colleague Andy Slaughter, Labour shadow human rights minister, for the UK government to publish and rethink the extent of its memorandum of understanding with Saudi Arabia.
At the European level, serious questions have to be asked about the agreement on counter-terrorism cooperation between the EU and the Gulf states. International human rights groups say at least some of those executed by Saudi Arabia have been political dissidents rather than terrorists, convicted by closed trials which do not meet international standards.
Additionally, an independent legal opinion over civilian casualties caused by the bombing of Yemen, suggests EU countries are continuing to sell arms to Saudi Arabia in breach of the EU's code of conduct on arms exports.
The EU must urgently review whether our own human rights obligations are being fully respected in both cases, and to act accordingly.
Second, the severing of diplomatic relations with Iran by Saudi Arabia, and followed by other Gulf states, gravely impedes international efforts to work together on resolving the crises in Syria and elsewhere in the region.
The attack on the Saudi Arabian embassy in Tehran was unacceptable, but was condemned by the Iranians themselves. This weekend's Arab League statement making a further one-sided condemnation simply deepens the rift, and can only further aggravate the alarming rise of Shia-Sunni sectarianism. This could fuel further conflict within the countries of the region as well as between them.
For Europe, the consequence will be more conflict on our doorstep, more refugee movements, and more recruits to ISIS/Da'esh.
The task for European diplomacy to seek to de-escalate tensions between Tehran and Riyadh has simultaneously become more difficult but more urgent. The EU should not cut ties to Saudi Arabia, but neither should we be deflected from full implementation of the nuclear agreement with Iran.
However difficult it might seem today, Europe must not lessen efforts to get all sides around the table to create a peace process for Syria. These executions must be condemned, but they do not have to be a catalyst for further catastrophe.
And we can show Saudi Arabia, Iran and all countries in the world who continue to use the death penalty, that Europe is genuinely open to all interests in the world in the cause of peace and development, but that we will not compromise on principles of respect for human rights.