The United States government on Wednesday approved a $1.1 billion deal to service Qatar's F-15 fighter jets despite the diplomatic stand-off between the Gulf emirate and its neighbors.

Qatar, home to one of the largest US military bases in the Middle East, is locked in a bitter dispute with Washington's other Arab allies in the region, led by Saudi Arabia.

US President Donald Trump took Riyadh's side in June when Saudi Arabia, Bahrain, the United Arab Emirates and Egypt cut diplomatic ties with Qatar, accusing it of supporting terrorism.

But Secretary of State Rex Tillerson has taken a more cautious line, attempting to broker an agreement to cool ties and build a regional front against Iranian influence and extremism.

On Wednesday, the State Department announced it had approved a $1.1 billion contract to service Qatar's F-15QA jets and build them ground facilities and hardened bunkers. 

"Qatar is an important force for political stability and economic progress in the Persian Gulf region," the department said, in a note from its Defense Security Cooperation Agency.

"Our mutual defense interests anchor our relationship and the Qatar Emiri Air Force plays a predominant role in Qatar's defense."

The new maintenance and training facilities will also come with improved "cyber security services, mission critical computer resources, support services, force protection services." 

Tillerson visited both Riyadh and the Qatari capital Doha last month in an effort to curb Iran's influence in the region and urge the Arab monarchies to negotiate away their differences.