Prime Minister Scott Morrison said while New Zealand has made no official request the Australian government was open to taking him back.
Ukrainian media reported that gunshots could be heard at the scene. It wasn't immediately clear whether anyone has been injured.
Police did not provide a motive for the killings. Canadian Prime Minister Justin Trudeau said the gunman killed at least 18.
Police first announced that they had arrested shooter Gabriel Wortman, 51 at a gas station in Enfield, outside Halifax, but later said he had died.
Twenty-six people including civilians -- the youngest a 13-year-old boy -- and security forces were killed by the rogue soldier, said Thailand's prime minister Prayut Chan-O-Cha.
There is roughly one school shooting a week in the United States, according to Everytown for Gun Safety, an organization that is pushing to limit the proliferation of firearms in the country.
The rap sheet against Redouane Lakdim, who lived in nearby Carcassonne, eventually drew deeper scrutiny by investigators worried he was at risk of Islamic radicalisation.
French President Emmanuel Macron said all evidence suggested that it was a terror attack — the first one since he became president in May.
Administrators considered him enough of a potential threat that one teacher said a warning was emailed last year against allowing him on the campus with a backpack.
Authorities say a series of shootings in rural Northern California left five people dead, including the shooter, and that two children were among the wounded.
Unlike their civilian counterparts, military judges and juries don't use sentencing guidelines. The result is often widely disparate sentences for the same or similar offenses.
Devin Patrick Kelley, who killed 26 people in a church shooting, went through the pews looking for survivors to execute and his first targets were children.
The latest US mass shooting again raised questions about gun control but President Donald Trump dismissed them and instead praised a gun-owner who opened fire in an effort to stop the killer.
The gunman, a 26-year-old veteran who had faced a court-martial and was dishonorably discharged from the Air Force, was found dead in his car which had crashed.
Stephen Paddock, the man who killed 59 concert-goers in Las Vegas was 64 years old, much older than the other mass shooters of recent infamy, all of whom were less than 30 years old.