India on Sunday night summoned the British deputy high commissioner and demanded an explanation over the complete "absence of security" after videos of pulling down of the Indian flag at the Indian mission in London during a protest by pro-Khalistan elements emerged on social media.

In a strongly-worded statement, the Ministry of External Affairs (MEA) said India finds "unacceptable" the indifference of the UK government to the security of Indian diplomatic premises and personnel in the UK.

British Deputy High Commissioner Christina Scott was summoned to the MEA in view of the incident as High Commissioner Alex Ellis was out of Delhi, sources said.

"The senior-most UK diplomat in New Delhi was summoned late evening today to convey India's strong protest at the actions taken by separatist and extremist elements against the Indian High Commission in London earlier in the day," the MEA said.

"An explanation was demanded for the complete absence of the British security that allowed these elements to enter the high commission premises," it said.

The MEA said the diplomat was reminded of the basic obligations of the UK government under the Vienna Convention.

"India finds unacceptable the indifference of the UK government to the security of Indian diplomatic premises and personnel in the UK," the MEA said.

It sought immediate steps to identify, arrest and prosecute those involved in today's incident.

"It is expected that the UK government would take immediate steps to identify, arrest and prosecute each one of those involved in today's incident, and put in place stringent measures to prevent the recurrence of such incidents," the MEA added.

In a tweet, High Commissioner Ellis said, "I condemn the disgraceful acts today against the people and premises of the @HCI_London - totally unacceptable." Images of shattered windows and men climbing the India House building were circulating on social media and videos from the scene showed an Indian official grabbing the flag from a protester through the first-floor window of the mission, while the protester was seen waving a Khalistani flag hanging off its ledge.

Scotland Yard said it was "aware" of an incident in the area but is yet to issue an official statement.

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