The New Zealand prime minister said she was "absolutely gutted" to hear of the stabbings.
A 50-year-old man has been arrested after a man was killed in north-west London on Sunday afternoon.
A suspect has been arrested, police in France said.
Six people were injured during the attack in a hotel on Friday afternoon.
Police have released new photos of Bibaa Henry and Nicole Smallman taken in the Wembley park on the night of the fatal stabbings.
He was one of three men in their twenties to be stabbed to death in 24 hours in London.
Nottinghamshire Police say injuries are not believed to be life-threatening as cordon set up inside cinema.
Two people have been arrested.