Qatar says the United Arab Emirates' alleged hacking of its government websites is a violation of international law.
US spies accused the UAE of infiltrating the sites to plant fake news and provoke one of the worst diplomatic rifts in recent Middle East history.
Qatar has been ostracised by its neighbours since reports revealed its emir making comments praising Hamas and calling Iran an "Islamic power".
The spat has wiped billions off stock values, separated families and raised doubt about Arab solidarity in the fight against Islamic State.
However, US intelligence agencies claim the quotes were posted falsely and deliberately in a state-sponsored hack ordered by the UAE to whip up anger against its smaller Gulf neighbour.
The Washington Post reports that new intelligence reveals the UAE government met to discuss the hacking plot and its execution on 23 May.
The next day President Trump, on a trip to Saudi Arabia, held a counter-terrorism meeting with Gulf Arab nation leaders, and shortly after that meeting the hacking operation was allegedly put into action.
Qatar says it believes the Washington Post report, saying it "unequivocally proves that this hacking crime took place".
:: Qatar accuses neighbours of terrorism hypocrisy
It is not clear if the UAE government's intelligence agencies carried out the hack or hired contractors to do so.
Gulf governments have, for instance, paid billions in lucrative surveillance contracts with Western security firms to spy on their own people.
News agencies and channels with close ties to the UAE, Saudi and Egyptian governments reported the emir's quoted comments with startling speed soon after the alleged hack took place.
US spies now believe those comments to have been concocted and planted on Qatari government websites.
The reports plunged the region into a diplomatic maelstrom that continues to ravage relations in the region.
Qatar has been subjected to a diplomatic and economic blockade that the US government says could compromised US efforts against so-called Islamic State.
:: Trump drops diplomatic clangers over Qatar
Qatar's antagonists accuse it of supporting terrorism and giving a home to extremists inciting violence and radicalisation.
The small but fabulously wealthy gulf kingdom is also regarded as too close to Iran, by its neighbours.
The UAE's government has denied any involvement in the hacking but the allegations from a respected newspaper with impeccable intelligence sources spell trouble for the coalition against Qatar.
Initially the US seemed to have taken sides with them against Qatar in the dispute, President Trump accusing the Qataris of funding terrorism "at the highest level".
But the Trump administration has sought a more even-handed approach since. Qatar's critics are widely thought to have overreached in their demands, in particular in their insistence the Al Jazeera news network be shut down.
With US spy agencies now apparently briefing against them, Qatar's antagonists may conclude US sympathy for their position is rapidly dwindling.