The National Investigating Agency has taken over the investigation into the attacks carried out by Khalistan supporters on Indian missions in the United States and Canada in March, police sources said on Saturday.
Earlier, the probe into violent protests and attempted vandalisation at the Indian High Commission in London in March this year was also handed over to the agency.
The Delhi Police's Special Cell had registered FIRs under the Unlawful Activities (Prevention) Act (UAPA) in connection with the attacks which took place in March, sources said.
The investigation has now been transferred to the NIA, they added.
A group of pro-Khalistan protesters had attacked and damaged the Indian Consulate in San Francisco. Raising slogans, the protesters broke open the makeshift security barriers installed by the city police and put up two so-called Khalistani flags inside the Consulate premises. Two consulate personnel soon removed these flags.
India had lodged a strong protest with the US Charge d'Affaires in Delhi.
The government had also summoned the Canadian High Commissioner and conveyed its strong concerns about the targeting of Indian diplomatic missions in Canada.
On June 12, the NIA released CCTV footage of the attack on the Indian Mission in London and sought the help of the public in identifying the culprits.
Pro-Khalistani protestors tried to vandalise the Indian High Commission in London and pulled down the national flag while holding protests outside the high commission complex on March 19.
It happened a day after Punjab Police launched a crackdown against radical preacher Amritpal Singh in Punjab.
Officials from the Mission had said the "attempted but failed" attack was foiled and that the tricolour was now flying "grander".
The Metropolitan police said that two members of security staff sustained minor injuries which did not require hospital treatment.
India had summoned the British deputy high commissioner based in New Delhi and demanded an explanation for the complete "absence of security".
In a strongly-worded statement, the Ministry of External Affairs had said India finds "unacceptable" the indifference of the UK government to the security of Indian diplomatic premises and personnel.
