Doha signed an agreement Wednesday with Washington to buy $12 billion USD worth of F-15 jets, according to Qatar’s defense ministry.

Defense Minister Khalid Al Attiyah and his U.S counterpart, James Mattis signed the deal in Washington, the Qatar News Agency said.

The Pentagon said in a statement the deal "will give Qatar a state of the art capability and increase security cooperation and interoperability between the United States and Qatar”.

The U.S Congress agreed last year to sell fighter jets to Qatar while the latest deal came after a recent Gulf crisis began between some Arab states and Qatar.

Two U.S warships arrived in Qatar’s Hamad Port on Wednesday to conduct a joint military drill but details have not been shared, Qatar News Agency was quoted.

Last week, five Arab countries - Saudi Arabia, Egypt, the United Arab Emirates, Bahrain and Yemen - cut off ties with Qatar, accusing Doha of supporting terrorism.

Qatar has denied the accusations, calling the moves to diplomatically isolate it “unjustified”.

Turkey has said that it stands with the tiny Gulf state against sanctions and has urged Riyadh to take the lead in finding a solution to the crisis.

Meanwhile, the UN human rights chief Wednesday warned of possible human rights violations in the wake of the diplomatic and economic isolation of Qatar.

“I am alarmed about the possible impact on many people’s human rights in the wake of the decision by Saudi Arabia, the United Arab Emirates (UAE), Egypt and Bahrain to cut diplomatic and economic ties with Qatar," UN High Commissioner for Human Rights Zeid Ra’ad Al Hussein said in a statement.

"It is becoming clear that the measures being adopted are overly broad in scope and implementation," Hussein said.

Qatar, for its part, has denied the accusations, calling the moves to diplomatically isolate it “unjustified”.

"We are receiving reports that specific individuals have already been summarily instructed to leave the country they are residing in, or have been ordered to return home by their own government," Hussein said.

"I am also extremely troubled to hear that the UAE and Bahrain are threatening to jail and fine people who express sympathy for Qatar or opposition to their own governments’ actions, as this would appear to be a clear violation of the right to freedom of expression or opinion," he said.