Clue: Seen regularly, harbour in Kuala Lumpur (it's somewhere in Asia) (5)
Answer: KABUL
Explanation: Definition: it's somewhere in Asia
An envelope ('in') of ABU ('seen regularly h**A**r**B**o**U**r') in KL ('Kuala Lumpur' – the abbreviation is even given in Chambers, and, of course, there is our contributor KLColin, until and unless he moves again).