ICAO Doc 4444
8.9.6.1.8 An aircraft making a radar approach should:

a) be directed to execute a missed approach in the following circumstances:

i) when the aircraft appears to be dangerously positioned on final approach; or
ii) for reasons involving traffic conflictions; or
iii) if no clearance to land has been received from the procedural controller by the time the aircraft reaches a distance of 4 km (2 NM) from touchdown or such other distance as has been agreed with the aerodrome control tower; or
iv) on instructions by the aerodrome controller; or

b) be advised to consider executing a missed approach in the following circumstances:

i) when the aircraft reaches a position from which it appears that a successful approach cannot be completed; or
ii) if the aircraft is not visible on the situation display for any significant interval during the last 4 km (2 NM) of the approach; or
iii) if the position or identification of the aircraft is in doubt during any portion of the final approach.

In all such cases, the reason for the instruction or the advice should be given to the pilot.