Cut off oil supply for capital (7)

I believe the answer is:

tripoli

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'for capital' is the definition.
(capital of Libya)

'cut off oil' is the wordplay.
'cut' becomes 'trip' (I can't explain this - if you can you should give a lot more credence to this answer).
'off' indicates an anagram.
'oil' is an anagram of 'oli'.
'trip'+'oli'='TRIPOLI'

'supply' is the link.

Can you help me to learn more?

(Other definitions for tripoli that I've seen before include "North African port" , "powdery deposit" , "Lebanese port" , "Place in Libya" , "North African capital" .)

I've seen this clue in The Guardian.

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