NYPD: Two women wanted for assault on 4 train

Police are searching for two women they say are responsible for assaulting a woman on a southbound 4 train.  
According to the NYPD, a 30-year-old woman was approached on the southbound 4 train in Brooklyn by the two suspects, who began punching and kicking her. The two suspects then exited the train at the Grand Army Plaza subway station.  
The victim suffered significant bruising and scratches but is expected to be OK.
It was not immediately clear what provoked the attack.