Her attacker may have fled in a southbound train, NYPD officials said. View Full Caption DNAinfo/Trevor Kapp

MANHATTAN — A 71-year-old woman was slashed across the face on a D train as it entered the Bleecker Street subway station in an unprovoked attack during Monday morning's commute, sources said.

The woman, whose name not immediately released, was on the train with the suspect, who is between 18 and 20, who walked up to her as it pulled into the station about 7:20 a.m., slashed her face and calmly walked off, sources said.

The woman had a four inch cut to the left side of her face and was treated at Bellevue Hospital, sources said.

Police said the suspect, who wore red pants and black sneakers, may have fled on a southbound D train, which stops in an adjoining station.

Witnesses noticed that he had been riding the train since before 79th Street, where they got on, sources said.

Monday's attack is another in a spate of unrelated but similar slashings.

Kari Bazemore walked up behind a woman in Chelsea and slashed her face from her nose down her lip on Jan. 1, police said. He was arrested about 12 hours later.

Francis Salud slashed a man across the face in the East Village on Jan. 16, police said. He was arrested Jan. 21, police said.