Washington (CNN) The top Republican and Democrat on the Senate armed services committee are asking Defense Secretary James Mattis to investigate accusations of torture at prisons in Yemen run by United Arab Emirates forces where US forces were also interrogating prisoners.

Sens. John McCain of Arizona and Jack Reed of Rhode Island sent a letter to Mattis on Thursday asking him to investigate the alleged abuses, which were revealed in an Associated Press report Thursday.

"We request that you direct an immediate review of the facts and circumstances related to these alleged abuses, including US support to the Emirati and Yemeni partner forces that were purportedly involved," the senators wrote in the letter, obtained by CNN.

"We also request that you conduct a thorough assessment of what, if anything, US forces knew about these alleged abuses or subsequently learned about them," they added.

The Associated Press reported there was a network of 18 prisons run by UAE or Yemeni forces, and that US forces participate in interrogations, although no instances were found where US forces participated in abuses.

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