Approach clearance
 

Situation:
Aircraft has clearance direct to á IAF, 20NM before the IAF the aircraft gets the approach clearance but not via IAF.
Question:
Is the aircraft allowed to intercept the approach after the IAF, for example at the IF?
Please reference ICAO documents to state your case.

I think it is a matter of comment sense. Any clearance must be unambiguous and contain the specific. If the published approach is to be modified then this should be by agreement but following a request from the pilot. ATC can of course make an offer but this must be accepted by the pilot. Therefore if the initial clearance is via the IAF then this should be continued unless the later clearance specifies not: i.e. "cleared to route direct" to a specific point. The oldest rule is, of course, ask if if the clearance is not clear.

Thank you for your answer, I agree with common sense but I can't find any rule/regulation that says so.

i believe you wont find any. This is more about the common sense. Common sense and proper airmanship should be to clarify misunderstandings between ATC and pilot. If you do not clarify, you can find yourself in the swiss cheese hole.

An approach starts at the IAF so there is no other option unless stated by ATC.

I agree with Markos, ICAO Pans-Ops 8168 Vol 1 defines an approach as starting at the IAF. Without any other instructions. You commence it there unless cleared to start it at the IF.

Cleared to a IAF.
Cleared for the Approach.

The second clearance is an addition to the first clearance. You are still cleared to the IAF.

The ATC controllers are watching your radar return and waiting with your approach clearance till they are assured the aircraft is heading to the IAF.

Scenario:
You are on radar vectors on a heading away from the IAF ( like on an extended downwind).
ATC clears you to the IAF.
Once you are on a heading towards the IAF you receive the Approach clearance (from that fix).

Thank you all for your comments :)