It ran Nato ragged as an expression of frustration (9)

I believe the answer is:

tarnation

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'expression of frustration' is the definition.
The definition suggests a singular noun which matches the answer.

'it ran nato ragged' is the wordplay.
'ragged' indicates anagramming the letters.
'it'+'ran'+'nato'='itrannato'
'itrannato' anagrammed gives 'TARNATION'.

'as an' acts as a link.

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I've seen this clue in The Guardian.

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