Shameer, I can see that crack has developed near the un-supported end of the beam. It can be due to the deflection of the beam at the end. It can also be due to improper bonding between the beam/slab and the wall above. It will be better if some closeup images are provided, as it is not clear from the images you attached.
Once the real cause is known, we can go for the solution. Right now, the solution seems to be to break the plaster and then fill the gap or cracks.