Abu Dhabi Crown Prince Mohammed bin Zayed tweeted that his talks with Mattis covered "the enhancing of defence and military ties" and "issues of mutual interest." He did not give further details.

Their talks were also reported by the UAE's official WAM news agency, which did not give further details either.

Mattis's August 28 warning that Washington could end its support for the intervention in Yemen the UAE and Saudi Arabia have spearheaded since March 2015 came amid an international outcry over the deaths of dozens of children in coalition air raids last month.

Twin strikes south of the rebel-held Red Sea port of Hodeida on August 23 killed 26 children, the UN said.

An August 9 strike in the rebel heartland of Saada province killed 51 people, 40 of them children, according to the Red Cross.

The US provides weapons, aerial refuelling and intelligence and targeting information to the coalition.

"It is not unconditional," Mattis said. "Our conduct there is to try and keep the human cost of innocents being killed accidentally to the absolute minimum."

The UAE is also a key US ally in the long-running campaign against Al-Qaeda's Yemen-based affiliate, regarded by Washington as its most dangerous.

While US action has largely been confined to air strikes and missile strikes from warships, UAE troops have conducted ground operations against the jihadists alongside allied Yemeni militia, ousting them from the southeastern port city of Mukalla.