US Defence Secretary Jim Mattis welcomed his Qatari counterpart Khalid al-Attiyah to Washington on Wednesday for the signing of the agreement for the sale of F-15 fighters.
After the Gulf countries moved against Qatar, US Secretary of State Rex Tillerson initially declined to take sides in the crisis, but his cautious stance was overshadowed nearly immediately by Mr Trump, who sent a series of tweets that appeared to take credit for and to praise the decision.
On Wednesday, the Pentagon emailed a statement, saying that the sale "will give Qatar a state-of-the-art capability and increase security cooperation and interoperability between the United States and Qatar".
The U.S. military announced a similar $21.1 billion deal in November for 72 F-15QA fighter jets for Qatar in the waning days of the Obama administration.
Attiyah said the agreement would boost Qatar's defences and create 60,000 jobs in the United States.
Boeing which is the maker of these fighter planes did not comment on the controversial sale.
A Qatari defense ministry source said the deal was for 36 jets. "America's support for Qatar is deep-rooted and not easily influenced by political changes".
Qatar is an important base for the U.S. military carrying out operations against Islamic State militants and other groups in Iraq, Syria, Afghanistan and beyond.
Separately US diplomats and secretary of state Rex Tillerson have taken a more balanced approach given the complexities of the dispute and Qata'rs hosting of a US base that is key to its efforts against ISIL and home to some 10,000 troops. More than 100 aircraft operate from there, according to Al Jazeera. The minister also said he would visit Kuwait later on June 14 and meet Saudi Arabian King Salman bin Abdulaziz al-Saud on June 16 in Mecca.
The UN aviation agency says it is reviewing Qatar's request to intervene in a diplomatic spat which has seen a Saudi-led bloc close its airspace to flights from Doha.
Gulf states transport ministers and aviation officials kicked off a meeting on Thursday at the United Nations aviation agency's headquarters in Montreal to discuss the airspace standoff resulting from the Arab world's biggest powers decision to cut ties with Qatar.
USA officials Secretary of State Rex Tillerson have called for the crisis to be de-escalated and on Wednesday while appearing before the House foreign affairs committee, said reports.