Why Qatar is the focus of terrorism claims
The dispute that has seen Saudi Arabia and its Gulf allies isolate Qatar stems from allegations that the tiny gas-rich nation is sponsoring extremist groups which are destabilising the Middle East.
This is not the first time Qatar's neighbours have expressed their displeasure over its individualist foreign policy - diplomatic relations were severed for nine months in 2014.
Tensions have arisen from Qatar's support for the Islamist Muslim Brotherhood; its close relationship with groups such as the Taliban and certain al-Qaeda affiliates; and its relationship with Iran, which has most recently led to allegations from Saudi Arabia that the state-funded broadcaster Al Jazeera is supporting Houthi rebels in Yemen fighting government forces backed by Saudi Arabia and the United Arab Emirates.
Doha has strongly denied Riyadh's accusations, and said it has taken more robust counter-terrorism measures than some of its neighbours.
Yet this latest row is shining a particular light on the role Qatar plays with its immense wealth.
In April, it reportedly paid a ransom of as much as $1bn (£790m) to a former al-Qaeda affiliate in Syria and to Iranian security officials as part of a deal that resulted in the release of 26 royal family members reportedly kidnapped by Iranian-backed Iraqi Shia militiamen and of dozens of Shia fighters captured by jihadists in Syria.
Thus it is Qatar's alleged continued funding of radical ideology and extremism that is seemingly the cause of concern this time.
'Way to go'
Since 9/11, the United States-led global effort to disrupt terrorist financing has been relentless. Domestic laws and United Nations Security Council Resolutions have been passed; entities and individuals have been subject to national and UN sanctions; and suspected conduits for terrorist funding, such as remittance companies and charities, have been shut down.
But despite all this, the commitment of some key nations, including Qatar, has been repeatedly questioned.
In 2014, then-US Treasury Under-Secretary for Terrorism and Financial Intelligence David Cohen noted: "Qatar, a long-time US ally, has for many years openly financed Hamas, a group that continues to undermine regional stability. Press reports indicate that the Qatari government is also supporting extremist groups operating in Syria."
He also drew attention to the "permissive" environment in Qatar that allowed fundraisers to solicit donations for extremist groups such as al-Qaeda and so-called Islamic State.
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In 2016, Mr Cohen's replacement at the US treasury department, Adam Szubin, noted that despite showing willingness to take enforcement action against terrorist financiers, Qatar had "a way to go" and lacked "the necessary political will and capacity to effectively enforce their counter-terrorism finance laws against all terrorist financing threats".
In response to these failings, the US has sanctioned several Qatari citizens for financing terrorism.
Yet despite leading the opposition to Qatar's financial activities - and no doubt emboldened by the recent visit to Riyadh by US President Donald Trump - Saudi Arabia has not escaped similar criticism.
Fifteen of the 19 aircraft hijackers on 9/11 were Saudi citizens; diplomatic cables from 2009 published by Wikileaks reflect regular US frustration at the difficulty of persuading the Saudi government to treat terrorist financing donors as a strategic priority; and the country has used its considerable hydrocarbon wealth to propagate its fundamentalist Wahhabi strain of Islam via schools and mosques around the world which have been accused by some of being a source of extremism.
Although a small number of individuals and entities in Saudi Arabia are alleged to have financed terrorism, the country is seemingly on much more supportive ground than Qatar, and is recognised for its efforts.
Indeed, during President Trump's visit, the US and Saudi governments announced the inauguration of a jointly-led regional Terrorist Financing Targeting Centre to counter new and evolving threats from terrorist financing, perhaps reflecting the extent to which Saudi Arabia has, in Washington's view, moved from being a terrorist financing problem to a key part of the solution in the Gulf region.
Yet this apparent commitment by Saudi Arabia to tackle terrorist financing may not be enough.
Although the direct financing of terrorist groups has unsurprisingly been the primary focus of policymakers and security authorities, more recently attention has expanded to include those who fund organisations and individuals who promote radical or extremist ideologies.
Speaking in December 2015 during a House of Commons debate on extending UK bombing of so-called Islamic State from Iraq into Syria, then-Prime Minister David Cameron committed to "establish a comprehensive review to root out any remaining funding of extremism within the UK... [examining] the nature, scale and origin of the funding of Islamist extremist activity in the UK, including any overseas sources".
Recent media reports suggest that, whilst completed, this review is unlikely to be made public.
Which brings us back to the current state of Gulf affairs.
The suggestions are that, as before, this crisis will quickly pass. But the increased focus this spat has brought to the financing of terrorism and extremist ideology will endure and, however unreasonable it believes this to be, Doha can expect to remain the centre of intense suspicion.
Tom Keatinge is director of the Centre for Financial Crime & Security Studies at the Royal United Services Institute (Rusi). Follow him on Twitter