In general,

Is it allowed to bowl chain (continuous) overs in international matches?

If Yes,
How many overs can the bowler bowl continuously?

If No,
Is it not allowed from the beginning of international cricket history or did the ICC ban it recently?

Consider the following situation:

If a bowler bowls first over, then an another bowler bowls two or three deliveries of the second over and can't continue bowling due to injury.

Now will the first bowler be allowed to bowl the remaining balls of this second over?