Canada on Monday ordered an Indian diplomat to leave the country after accusing the Indian government of being involved in the killing of a Canadian Sikh leader in British Columbia in June.
Canadian Prime Minister Justin Trudeau said that an investigation into "credible allegations" that Indian state actors could be behind the death of Hardeep Singh Nijjar, was ongoing.
India rejected the accusations, calling them "absurd and motivated."
Ottawa's diplomatic expulsion prompted New Delhi to announce on Tuesday that a Canadian diplomat in India has been given a five-day notice to leave the country.
The accusations sent already sour relations between the two countries to a dramatic new low.
Canada: If true, 'violation of our sovereignty'
Regarding the allegations, Ottawa's Foreign Minister Melanie Joly said: "If proven true this would be a great violation of our sovereignty and of the most basic rule of how countries deal with each other."
Canada is home to hundreds of thousands of people of Indian origin, many of whom are Sikhs.
The White House National Security Council spokesperson Adrienne Watson said in a statement the United States was "deeply concerned about the allegations" made by Canada.
"We remain in regular contact with our Canadian partners. It is critical that Canada's investigation proceeds and the perpetrators be brought to justice," the statement read.
India rejects allegations
India's Ministry of External Affairs said in a statement that such "allegations seek to shift the focus from Khalistani terrorists and extremists, who have been provided shelter in Canada and continue to threaten India's sovereignty and territorial integrity."
Further, in a tit-for-tat move, India expelled a Canadian diplomat.
"The decision reflects the government of India’s growing concern at the interference of Canadian diplomats in our internal matters and their involvement in anti-India activities," said the foreign ministry.
Who is the Sikh leader in question and what is the issue?
Hardeep Singh Nijjar was shot on the premises of a Sikh temple in Surrey, British Columbia, in June of this year.
Nijjar was declared a terrorist by the Indian government a few years ago because of his activism for a separate homeland for Sikhs in the Punjab region of India.
The fight for a separate Sikh state or the "Khalistan" movement has its roots in the partition of the Indian subcontinent along religious lines.
The 1947 partition sent Muslims to the newly created Pakistan and Hindus and Sikhs to India. Punjab province, which was divided between India and Pakistan, saw deadly violence.
The Khalistan movement was crushed by the Indian government in the years that followed, especially in the 1980s. The decade saw violent anti-Sikh riots that killed thousands, and the movement was banned, with Indian officials citing it as a security threat.
Trudeau spoke to Modi at G20
The Indian government had put Nijjar on a wanted list and accused him of being actively involved in the networking and training of the separatist group he headed.
Many in Canada and elsewhere alleged that the Indian government was behind the death of Nijjar. Trudeau said intelligence agencies were looking into those allegations.
"Over the past number of weeks Canadian security agencies have been actively pursuing credible allegations of a potential link between agents of the government of India and the killing of a Canadian citizen, Hardeep Singh Nijjar," Trudeau said.
Trudeau added that he brought up the slaying with Modi at the G20 summit. Trudeau said he told Modi that any Indian government involvement would be unacceptable and that he asked for cooperation in the investigation.
The Indian government in its response to the conversation between the leaders said that allegations at the time were also "completely rejected."
rm/jsi (AP, Reuters, AFP)