Four separate attacks on the A train line between Friday and early Saturday, two of them deadly, have prompted the deployment of more than 500 police officers throughout the New York City Transit stations.

Subway riders should expect to see an escalated police presence immediately.

Investigators say an unknown man stabbed a 67-year-old man Friday morning at 11:20 a.m., at the 181st Street A train station. That victim is recovering in a nearby hospital.

Around 11:30 p.m. Friday, a man was found dead with stab wounds to the neck and torso on an A train at the Mott Avenue subway station.

Hours later, at 1:15 a.m. Saturday, a woman was found inside an A train at West 207th Street and Broadway with multiple stab wounds. She was pronounced dead.

Then around 1:30 a.m. at the West 181st Street train station, a 43-year-old man was found with stab wounds. He's in stable condition.

Investigators are looking into the connection between the four attacks and hope to release an image of the suspect soon.

Transit and union officials released a joint statement, saying, "The recent horrifying attacks in the subway system are outrageous and unacceptable. Every customer, and each of our brave, heroic transit workers deserve a safe and secure transit system. The time for action is now. We are demanding that additional resources be put into the system to address this challenge immediately."

The increased police presence includes 75 plain clothed officers.