USA 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.
The spat has wiped billions off stock values, separated families and raised doubt about Arab solidarity in the fight against Islamic State.
The UAE's minister of state for foreign affairs Anwar Gargash said earlier on Monday that the Washington Post report was false and denied his country's involvement in any hack.
The cyber campaign ultimately resulted to a rupture in ties between Doha and five of its Gulf Arab neighbors led by Saudi Arabia.
Qatar said in late May that hackers had posted fake remarks by the emir, an explanation rejected by Gulf states.
The newspaper report, published online Sunday evening, cited unnamed USA intelligence officials.
Gulf governments have, for instance, paid billions in lucrative surveillance contracts with Western security firms to spy on their own people.
U.S. spies now believe those comments to have been concocted and planted on Qatari government websites.
Qatar has been subjected to a diplomatic and economic blockade that the USA government says could compromised U.S. efforts against so-called Islamic State. Funding, supporting, and enabling extremists from the Taliban to Hamas and Qadafi.
He indicated that the culprit was one of the Middle Eastern countries that carried out a boycott of Qatar in the fallout of the hack, including Bahrain, Egypt, Yemen and the UAE.
Trump, however, has firmly sided with Riyadh and its allies, calling Qatar a "high level" supporter of terrorism.
But the Trump administration has sought a more even-handed approach since. "They [the UAE] claim that basically their demands from Qatar are legitimate and they insist that they should be fulfilled nearly as a diktat instead of sitting at a table and negotiating some legitimate differences that they might have with Doha, and somehow, unfortunately, Saudi Arabia has followed suit", said Jahshan.
With US spy agencies now apparently briefing against them, Qatar's antagonists may conclude US sympathy for their position is rapidly dwindling.