Cops are grilling a suspect they believe was behind a horrifying stabbing on the Upper East Side this morning.

Law enforcement sources said the suspect was brought into the 19th Precinct stationhouse this evening. His name has not been released and charges are pending.

The attacker plunged his weapon into the victim’s stomach without provocation around 10:30 a.m., police said. The man then fled.

The victim, 25, did not know her attacker, police said. She was assaulted on Second Avenue near 86th Street and taken to Cornell Weill in stable condition.

Police are looking for the unkempt, unshaven suspect, believed to be 5’9″-5’11” and in his 40s.

The victim was crossing the street when the man tried to mug her, police said.

“He tries to take her bag and she resists,” Police Commissioner Ray Kelly said. “He stabs her. He may also have sprayed her with some sort of substance.”

No weapon was recovered, but investigators believe the assailant used a knife.