The United States and Britain called on India to reconsider its demand for Canada to reduce its diplomatic staff in India, voicing their apprehension after Ottawa withdrew 41 diplomats amid a row over Sikh separatist leader Hardeep Singh Nijjar’s killing, Reuters reported.

Canada has accused India of being involved in the murder of Canadian citizen and Khalistani militant Hardeep Singh Nijjar in a Vancouver suburb in June. India has refuted the accusation.

"We are concerned by the departure of Canadian diplomats from India, in response to the Indian government's demand of Canada to significantly reduce its diplomatic presence in India," US State Department spokesperson Matthew Miller said, according to the Reuters report.

"Resolving differences requires diplomats on the ground. We have urged the Indian government not to insist upon a reduction in Canada's diplomatic presence and to cooperate in the ongoing Canadian investigation. We expect India to uphold its obligations under the 1961 Vienna Convention on Diplomatic Relations, including with respect to privileges and immunities enjoyed by accredited members of Canada's diplomatic mission," the statement said.

The United States and the United Kingdom have emphasised that they treat Canada's accusations seriously and, in tandem with London, have called on India to collaborate with Canada in the investigation of the murder, according to the Reuters report.

While Western powers have been cautious about openly censuring India, analysts suggest that the US and UK are cautious about jeopardising their relationship with India, which they see as a counterweight to their primary Asian rival, China.

Nonetheless, the recent remarks from the US State Department and the UK's Foreign Office are the most explicit criticism from Washington and London towards New Delhi regarding this matter so far.

"We do not agree with the decisions taken by the Indian government that have resulted in a number of Canadian diplomats departing India," a spokesperson for Britain's Foreign Office said.

After New Delhi asked Canada to reduce its diplomatic presence in India last month, giving a deadline of October 10 to complete the action, it recalled 41 diplomats from the country.

In response, Canada announced on Friday that it would temporarily halt in-person operations at consulates in various Indian cities and cautioned about potential delays in visa processing.

Britain's Foreign Office also cited the Vienna Convention. It said "the unilateral removal of the privileges and immunities that provide for the safety and security of diplomats is not consistent with the principles or the effective functioning of the Vienna Convention."

The Indian government had given Ottawa until October 10 to reduce Canadian diplomatic staff in that country to a level on par with the number of Indian diplomats in Canada.

A majority of the Canadian diplomats working in India outside of Delhi were evacuated to either Kuala Lumpur or Singapore, according to a CTV report.

MEA spokesperson Arindam Bagchi on October 5 said India has asked Canada to reduce diplomatic staff to "bring parity".

"Given the much higher diplomatic presence in India and their continuing interference in our internal affairs, we had sought parity in our respective diplomatic presence," Bagchi was quoted as saying by the news channel.

Amid the ongoing diplomatic row, India had asked Canada to recall 41 of its diplomats from the country by October 10.