A 26-year-old woman was seriously injured after her ex-boyfriend stabbed her in the back with a knife in Nanakuli Wednesday, Honolulu police said.

Police said the woman and her ex, a 33-year-old man, were involved in an argument in the 87-1700 block of Mohihi Street at about 4:05 p.m.

The argument escalated and the man stabbed the woman in the back with a knife. She was taken in serious condition to a hospital.

Police arrested the man at the scene on suspicion of first-degree attempted murder.

A day earlier, officers had issued an abuse warning citation to the suspect.

Police said the suspect was arrested Wednesday on suspicion of first-degree attempted murder instead of second-degree attempted murder because he violated the warning.