NEW DELHI (AP) — The U.S. has charged an Indian national in what prosecutors allege was a failed plot to assassinate a Sikh separatist at the behest of an unnamed Indian government official.

The charges announced Wednesday against an Indian national arrested in June in Europe come two months after Canadian Prime Minister Justin Trudeau said there were credible accusations that India may have been linked to the killing of a Sikh activist near Vancouver, straining relations between the two countries.

The U.S. case is particularly sensitive given the high priority that President Joe Biden placed on improving ties with India and courting it to be a major partner in the push to counter China’s increasing assertiveness.

India, which has banned the Sikh independence — or Khalistan — movement, denied having a role in the Canada killing and said it was examining information shared by the U.S. and taking those accusations seriously.

Here are some details about the issue:

WHAT IS THE KHALISTAN MOVEMENT?

India’s Sikh independence movement eventually became a bloody armed insurgency that shook India in the 1970s and 1980s. It was centered in the northern Punjab state, where Sikhs are the majority, though they make up about 1.7% of India’s overall population.

The insurgency lasted more than a decade and was suppressed by an Indian government crackdown in which thousands of people were killed, including prominent Sikh leaders.

Hundreds of Sikh youths were also killed during police operations, many in detention or during staged gunfights, according to rights groups.

In 1984, Indian forces stormed the Golden Temple, Sikhism’s holiest shrine, in Amritsar to flush out separatists who had taken refuge there. The operation killed around 400 people, according to official figures, but Sikh groups say thousands were killed.

The dead included Sikh militant leader Jarnail Singh Bhindranwale, whom the Indian government accused of leading the armed insurgency.

On Oct. 31, 1984, Prime Minister Indira Gandhi, who ordered the raid on the temple, was assassinated by two of her bodyguards, who were Sikh.

Her death triggered a series of anti-Sikh riots, in which Hindu mobs went from house to house across northern India, particularly in New Delhi, pulling Sikhs from their homes, hacking many to death and burning others alive.

IS THE MOVEMENT STILL ACTIVE?

There is no active insurgency in Punjab today, but the Khalistan movement still has some supporters in the state, as well as in the sizable Sikh diaspora beyond India. The Indian government has warned repeatedly over the years that Sikh separatists were trying to make a comeback.

Prime Minister Narendra Modi’s government has also intensified the pursuit of Sikh separatists and arrested dozens of leaders from various outfits that are linked to the movement.

When farmers camped out on the edges of New Delhi to protest controversial agriculture laws in 2020, Modi’s government initially tried to discredit Sikh participants by calling them “Khalistanis.” Under pressure, the government later withdrew the laws.

Earlier this year, Indian police arrested a separatist leader who had revived calls for Khalistan and stirred fears of violence in Punjab. Amritpal Singh, a 30-year-old preacher, had captured national attention through his fiery speeches. He said he drew inspiration from Bhindranwale.

HOW STRONG IS THE MOVEMENT OUTSIDE OF INDIA?

India has been asking countries like Canada, Australia and the U.K. to take legal action against Sikh activists, and Modi has personally raised the issue with the nations’ prime ministers. India has particularly raised these concerns with Canada, where Sikhs make up nearly 2% of the country’s population.

Earlier this year, Sikh protesters pulled down the Indian flag at the country’s high commission in London and smashed the building’s window in a show of anger against the move to arrest Amritpal Singh. Protesters also smashed windows at the Indian consulate In San Francisco and skirmished with embassy workers.

India’s foreign ministry denounced the incidents and summoned the U.K.’s deputy high commissioner in New Delhi to protest what it called the breach of security at the embassy in London.

The Indian government also accused Khalistan supporters in Canada of vandalizing Hindu temples with “anti-India” graffiti and of attacking the offices of the Indian High Commission in Ottawa during a protest in March.

Last year, Paramjit Singh Panjwar, a Sikh militant leader and head of the Khalistan Commando Force, was shot dead in Pakistan.