Afghanistan has accused Pakistan's military of targeting a Kabul hospital for drug abuse addicts in airstrikes, with the country claiming that more than 400 people were killed. Pakistan has dismissed the accusation, saying the strikes which were also conducted in eastern Afghanistan, did not hit any civilian sites. The attack came hours after Afghan officials said the two sides exchanged fire along their border, killing four people in Afghanistan, as the deadly conflict between the neighbours entered its third week. But why are the two countries fighting? Watch this to know.