Saudi Arabia, the United Arab Emirates, Egypt and Bahrain accused Qatar in a joint statement carried on Gulf state media of thwarting all efforts aimed at resolving the rift and said it intends to "continue its policy aimed at destabilizing security of the region."
They vowed to "take all necessary political, economic and legal measures" against Qatar in a "timely manner." They did not specify what those steps could include, though officials have previously suggested they could intensify efforts to isolate Qatar economically.
Qatar issued its response to the ultimatum in a hand- written letter from 37-year-old Emir Tamim bin Hamad Al Thani that was delivered earlier this week to Kuwait, which is mediating the crisis.
The contents of the letter have not been disclosed, but the anti-Qatar bloc described it as "negative" and failing to appreciate the gravity of the situation.
In a statement attributed to an unnamed senior foreign ministry official released later today, Qatar called allegations made by the quartet against it false and tantamount to "defamation in contradiction with the established foundations of international relations."
It said its position on terrorism "is consistent and known for its rejection and condemnation of all forms of terrorism whatever the causes and motives are." It went on to say that Qatar "is an active member committed to international conventions in combating terrorism and its financing at the regional and international levels.