The United Arab Emirates has denied it was behind the alleged hacking of Qatar's state news agency in May.
The Washington Post cited US intelligence officials as saying the UAE had orchestrated the posting of incendiary quotes attributed to Qatar's emir that he insisted were fabricated.
The incident helped spark a diplomatic rift between Qatar and its neighbours.
UAE Minister of State for Foreign Affairs Anwar Gargash said on Monday that the Post's report was "not true".
He also reiterated that the UAE and five other Arab nations had not written to Fifa to demand that Qatar be stripped of the right to host the 2022 World Cup.
Swiss news network The Local said a fake news story quoting Fifa president Gianni Infantino had been posted on a copycat website on Saturday.
The Washington Post's story cited unnamed US intelligence officials as saying newly-analysed information confirmed that on 23 May senior members of the UAE government had discussed a plan to hack Qatari state media sites.
Later that day, the official Qatar News Agency quoted Emir Sheikh Tamim bin Hamad al-Thani as criticising US "hostility" towards Iran, describing it as an "Islamic power that cannot be ignored", and calling Hamas the "legitimate representative of the Palestinian people".
Qatari officials said the agency had been hacked by an "unknown entity" and that the story had "no basis whatsoever". However, the remarks were reported across the region and caused a stir.
The UAE, Saudi Arabia, Bahrain and Egypt responded by blocking Qatari media.
Two weeks later, the four countries cut all links with Qatar over its alleged support for terrorism and relations with Iran. The boycott has caused turmoil in the oil- and gas-rich emirate, which is dependent on imports by land and sea for the basic needs of its population of 2.7 million.
The US intelligence officials told the Post it was unclear whether the UAE authorities had hacked the Qatar News Agency itself or paid a third party to do it.
The Guardian reported last month that an investigation by the US Federal Bureau of Investigation had concluded that freelance Russian hackers were responsible.
US intelligence agencies declined to comment on the Post's article, but the UAE's ambassador in Washington insisted that it "had no role whatsoever in the alleged hacking".
"What is true is Qatar's behaviour. Funding, supporting, and enabling extremists from the Taliban to Hamas and Gaddafi. Inciting violence, encouraging radicalization, and undermining the stability of its neighbours," Yousef al-Otaiba wrote in a statement posted on Twitter.