"What is true is Qatar's behavior. Inciting violence, encouraging radicalisation, and undermining the stability of its neighbours", the statement said.
Saudi Arabia and its allies imposed sanctions on Doha on June 5, including closing its only land border, denying Qatar access to their airspace and ordering their citizens back from the emirate.
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.
Qatar said in late May that hackers had posted fake remarks by the emir, an explanation rejected by Gulf states.More news: Real To Bid £50m For Man Utd Star — Reports
"The Washington Post story is not true, purely not true", he said responding to a question after a speech at Chatham House in London.
According the Washington Post, U.S. intelligence officials concluded United Arab Emirates arranged the cyber attack of Qatar's state-run news and social media sites, sparking a rift between Qatar and its neighbors in the Arab region.
The Federal Bureau of Investigation was previously known to be working with Qatar to probe the hacking.
With US spy agencies now apparently briefing against them, Qatar's antagonists may conclude US sympathy for their position is rapidly dwindling.
Khalil Jahshan, executive director at the Arab Center Washington, DC, told Al Jazeera the revelations are the most important development so far since the beginning of the crisis and undermined the Emirati position.
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. On June 22, four Arab states advanced 13 demands to Qatar for restoring relations and gave it a 10-day deadline to comply with them.
"So the failure, if you will, or at least temporary failure of Tillerson is not going to change unless there is a change of attitude on the part of the Emirates in particular".