Gulf residents are still in shock.

Qatar, a sovereign Arab state, is being subjected to unprecedented sanctions by its Gulf Arab neighbours, led by Saudi Arabia.

The punishing economic and diplomatic measures have been taken because of allegations that Qatar has persisted in funding terrorist groups and destabilising the region, both of which it denies.

So now airspace has been closed, imports stopped at borders, Qatari expatriates expelled.

The veneer of Gulf Arab unity, as embodied in the Gulf Co-operation Council (GCC), has worn off.

Even if, as expected, the immediate crisis is resolved by talks, the Gulf will never be the same again.

Now there are fears this action may push this region down a new and dangerous path.

The Trump factor

The action against Qatar has been initiated by Saudi Arabia, the United Arab Emirates, Bahrain and Egypt - four countries ruled by Sunni Muslim leaderships that see the world through the prism of two major threats to their rule: Iran and political Islam, coupled with violent jihad.

They accuse Qatar of encouraging both strands.

On Iran, the quartet's complaint appears to be excessive.

Qatar shares with Iran the world's largest natural gas condensate field - the offshore South Pars/North Dome Field.

Geography has made them neighbours, they need to get on.

But Saudi Arabia's rulers, encouraged by President Donald Trump's recent visit to Riyadh and his strong condemnation of Tehran, would prefer to see a united Gulf Arab stand against its arch rival Iran.

Qatar, in their eyes, is "letting the side down".

On political Islam, it is easier to see why the dynastic monarchies of the Gulf feel threatened by Qatar's actions.

Qatar's ruling family, the Al-Thani's, have long supported the Muslim Brotherhood, which espouses a pan-Islamic caliphate that would ultimately do away with current rulers.

Qatar has backed Islamist movements in Egypt, Libya, Syria and the Gaza Strip.

They have allowed the country's satellite TV channel, Al-Jazeera, to host vocal critics of Arab leaders, although not Qatar's.

The UAE Crown Prince, Sheikh Mohammed Bin Zayed Al-Nahyan, told me he sees the Muslim Brotherhood as an existential threat to the region.

Saudi troubles

On terrorism, the picture is more opaque.

Saudi Arabia and its allies accuse Qatar of funding terrorist groups, notably in Syria and Iraq.

A lot of people say this is a case of hypocrisy, of the pot calling the kettle black.

In a failed bid to topple Syria's President Bashar al-Assad, Saudi Arabia has itself funnelled hundreds of millions of dollars to hardline Sunni fighters in Syria, some of which has ended up in the hands of so-called Islamic State.

There is no denying though, that Qatar has had connections to the al-Qaeda-linked al-Nusra Front in Syria.

On one of my visits to the Qatari capital, Doha, Qatari intelligence officials personally told me in 2014 how they had successfully brought about the release of hostages held by this group.

That group would naturally have demanded something substantial in exchange.

In April this year it has been reported that a staggering $1bn (£784m) ransom was paid by Qatar to terrorist groups in Iraq, some of it to Iran, in order to secure the release of 26 princes kidnapped while hunting a large game bird called a bustard.

Qatar denies it.

While the action to isolate and punish Qatar reflects a joint view held by several countries, leading the charge is the 31-year-old Saudi Deputy Crown Prince and Defence Minister, Mohammed Bin Salman, known as MBS.

The question many are asking now is whether MBS has gone too far.

Saudi Arabia already has enough trouble on its hands.

Together with the UAE, it's spent the last two years fighting an inconclusive and deeply destructive war in Yemen.

It's coping with a simmering insurgency in its Shia-dominated Eastern Province.

It is still part of the US-led coalition against IS, a group that has already bombed several Saudi mosques and threatened more attacks only this month.

The real long term cost of isolating Qatar may well turn out to be economic.

To attract business and provide jobs for their swelling youth population, the Gulf Arab states need stability and a business-friendly environment.

It is hard to see how this stand-off could do more to damage this.

The longer it persists, the deeper the wounds, not just to Qatar and its tiny, affluent population, but to the entire region.