Prisoners put down, observed to be upset (9)

I believe the answer is:

internees

'prisoners' is the definition.
(internee is a kind of prisoner)

'put down observed to be upset' is the wordplay.
'put down' becomes 'inter' (interring is a kind of putting down**).
'observed' becomes 'seen' ('seen' can be a synonym of 'observed').
'to be upset' says the letters should be written backwards (I've seen 'being upset' mean this).
'seen' back-to-front is 'nees'.
'inter'+'nees'='INTERNEES'

(Another definition for internees that I've seen is " POWs".)

I've seen this clue in The Times.

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