The most common and most likely answer to this crossword clue is the 6 letter word TEHRAN
I've seen this crossword clue in The Guardian
T
E
H
R
A
N
More clues leading to the result TEHRAN
- What, in time, controlled capital
- What in time controlled capital
- Moving earth near new capital
- The bastard was in charge of Middle Eastern capital
- Eastern time in bronze capital
- The revolutionary fled the capital
- The suspect fled capital city
- I
- After short time what has managed to become country’s biggest city
- Capital city getting hit — what river floods it?
Buddy explains!

The straight part
We know that "capital" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case capital = tehran.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.