London bassist's inside a foreign area (7)

I believe the answer is:

donbass

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'area' is the definition.
(I know that Donbass is a area)

'london bassist's inside a foreign' is the wordplay.
'DONBASS' is hidden within the letters.
But, I am uncertain how the hidden word is indicated.

Can you help me to learn more?

I've seen this clue in The Times.

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