A $12bn deal to buy US F-15 fighter jets shows Qatar has deep-rooted support from Washington, a Qatari official said on Thursday, Reuters news agency reported.

Qatar is facing an economic and diplomatic boycott by Saudi Arabia and its regional allies who cut ties last week, in the worst rift among Gulf Arab states in years.

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They accuse Qatar of "funding terrorism", fomenting regional unrest and cosying up to their enemy Iran, all of which Qatar denies.

Trump has echoed the accusations against Qatar, even as his defence and state departments have tried to remain neutral in the dispute among key allies.

"This is of course proof that US institutions are with us but we have never doubted that," Reuters news agency quoted a Qatari official in Doha as saying.

"America's support for Qatar is deep-rooted and not easily influenced by political changes."

The Pentagon said the jets sale would increase security cooperation between the US and Qatar and help them operate together.

It added that US Defence Secretary Jim Mattis and Qatar's Defence Minister Khalid al-Attiyah had also discussed the current state of operations against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) and the importance of de-escalating tensions in the Gulf.

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Qatar hosts an important base for the US military carrying out operations against ISIL and other groups in Iraq, Syria, Afghanistan and beyond. Al Udeid Air Base is home to more than 11,000 US and coalition troops.

Two US warships arrived at Hamad port in Qatar on Wednesday as part of a planned joint military exercise involving marine forces, Qatar's state news agency said.

Turkish support

Turkish Foreign Minister Mevlut Cavusoglu, on a Gulf tour trying to help broker an end to the crisis, defended the fighter jet deal.

"Just like other countries, like Saudi Arabia, the United Arab Emirates, Egypt ... it is natural for Qatar to buy airplanes or parts necessary for its own defence," Cavusoglu said in Kuwait following talks with his Kuwaiti counterpart, according to Turkey's state-run Anadolu news agency.

Turkey is friendly to Qatar and has sent food supplies since the sanctions were imposed. Kuwait has led efforts to mediate the dispute.

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Source: News agencies