Can someone please tell me which sentence is correct ?
First, it depends on what are you trying to say. If you are trying to say that both A and B has done nothing then both sentence means the same. But, there is a difference which is listed below -:
no action has been observed either from A or from B.
This sentence means A or B has done nothing.
no action has been observed neither from A nor from B.
This sentence also means that A or B has done nothing. But, here some work was expected from both A and B.
The actual difference is made from the first word of the second sentence "no".
Moreover, i believe it's one of the best way of making these types of sentence.