Police are investigating after a woman who attended community meetings trying to tackle violent crime was stabbed to death in a street in north-west London.

The victim, in her 20s, was attacked in Belmont Street, Camden, just after 11pm on Sunday, and pronounced dead about 40 minutes later.

Police believe the attack followed a row in the street, with two other women suffering knife injuries.

A 35-year-old woman has been arrested on suspicion of murder, said police.

Terry Ellis, from Camden Against Violence, said the woman who died regularly came to meetings of the group, which he runs. “She was a wonderful young lady, always happy. She’s got a lovely son and was just a normal mother,” he said.

In a separate incident, a man in his 20s was found with a gunshot wound in Kentish Town, also in north-west London, after police, including armed officers, were called to reports of a shooting late on Sunday night.

Police said the two deaths were believed to be wholly unconnected.

The shooting in Kentish Town appeared to have the hallmarks of a targeted killing. Police said one or two people, on a moped or motorbike, drove by and opened fire at close range.

An air ambulance was sent to the scene, in Malden Road, but the man was pronounced dead shortly after midnight.

It was one of three knife and gun deaths in the British capital within 24 hours, each of which appear to be unrelated. In another incident, in south London, police believe a man may have accidentally shot himself.

The man, aged 25, was found at 3.45pm on Sunday in Sydenham Road, south-east London.

It is believed a gun in the man’s possession went off, the bullet hit a car or hard object, then ricocheted back and struck the man, leaving him with fatal injuries.

The death is being treated as unexplained, and not yet as a homicide, police said.

DCI Richard Leonard said: “We are still in the early stages of the investigation and our enquiries into how the man came to be fatally injured continue.

“However, one hypothesis is that the man unintentionally discharged a firearm resulting in his fatal injury.”

A man has been arrested in connection with the investigation and is in custody at a police station in south London.

The Metropolitan police said the number of homicides in London this year stood at more than 100.

The mayor’s office for policing and crime, which oversees the Met, said the figure stood at 99. Last year it recorded 135 homicides in London, and this year police were hoping for a reduction following intensified efforts and increased resources to combat serious violent crime.