Canadian police said on Friday that they have made three arrests in the killing of a Sikh separatist leader last June in suburban Vancouver.

The death of Hardeep Singh Nijjar became the centre of a diplomatic spat with India.

Royal Canadian Mounted Police Assistant Commissioner David Teboul said three suspects have been arrested and charged in the slaying of the 45-year-old by masked gunmen in Surrey, near Vancouver.

But he said police could not comment on nature of the evidence nor the motive.

“This matter is very much under active investigation,” Mr Teboul said.

Canadian prime minister Justin Trudeau sparked a diplomatic feud with India when he said in September that there were “credible allegations” of Indian involvement in the killing of Mr Nijjar.

India had accused Mr Nijjar of links to terrorism but angrily denied involvement in the slaying.

Nijjar, an Indian-born citizen of Canada, was a plumber and also a leader in what remains of a once-strong movement to create an independent Sikh homeland, known as Khalistan.

But he had denied allegations of ties to terrorism.

The three suspects are Indian nationals Kamalpreet Singh, Karan Brar and Karampreet Singh, and they were arrested in Edmonton, Alberta, Royal Canadian Mounted Police Superintendent Mandeep Mooker said.

“This investigation does not end here. We are aware that others may have played a role in this homicide and we remain dedicated to finding and arresting each one of these individuals,” Mr Mooker said.

A bloody decade-long Sikh insurgency shook north India in the 1970s and 1980s, until it was crushed in a government crackdown in which thousands of people were killed, including prominent Sikh leaders.

The Khalistan movement has lost much of its political power but still has supporters in the Indian state of Punjab, as well as in the sizable overseas Sikh diaspora.

While the active insurgency ended years ago, the Indian government has warned repeatedly that Sikh separatists were trying to make a comeback.