The deal was completed despite Qatar being criticised recently by US President Donald Trump for supporting terrorism, a charge that Qatar has denied.
Qatar's Ministry of Defence on Wednesday announced that the country has signed a $12 billion deal to buy F-15 fighter jets from the United States.
US Defence Secretary Jim Mattis and representatives from Qatar were set to meet on Wednesday to seal the agreement, a source familiar with the deal told Reuters. Bloomberg News reported the deal was for 36 jets.
In November, the US approved a possible sale of up to 72 F-15QA aircraft to Qatar for $21.1 billion. Boeing Co is the prime contractor on the fighter jet sale to the Middle East nation.
Boeing declined to comment.
Major US Ally
Meanwhile, two US Navy vessels arrived in Doha to take part in a joint military exercise with the Qatari Emiri Navy on Wednesday, Qatar news agency QNA reported.
Qatar, a major US ally, has been in the spotlight since four major Arab powers, including Saudi Arabia and Egypt, severed their ties with the country and accused it of supporting terrorism and working secretly with Iran, the arch-foe of the Saudis.
Qatar hosts the biggest US military base in the Middle East with 11,000 troops deployed to or assigned to Al Udeid Air Base. More than 100 aircraft operate from there.
The Pentagon last week renewed praise of Qatar for hosting a vital US air base and for its "enduring commitment to regional security," after four Arab countries cut ties with the Gulf ally.
The Pentagon reassurance differed from US President Donald Trump's comments that applauded the decision, via Twitter.
It was unclear if the arrival of the two warships was planned before the Gulf rift or if it was a sign of support from the Pentagon.
Qatari Navy officers received the crews of the two vessels, QNA said, citing a statement from the country's defence ministry.
Turkey sent its foreign minister to Qatar as part of a drive to resolve the crisis. Kuwait, a neighbour and a member of the Gulf Cooperation Council (GCC), also has been mediating.