The anti-terror unit of Delhi Police has started investigations into the bomb threat email sent to over 130 schools in the Delhi-NCR region, as the initial probe hinted at a deeper conspiracy by a terror group during the Lok Sabha elections, officials said on Wednesday.

A case has been registered under relevant sections of law for offences like conspiracy and threat by the Special Cell and a dedicated team formed to conduct the investigation, an official said.

"The matter is related to national security. It needs a deeper probe," the official said.

In a scare of unprecedented scale, over 130 schools in the Delhi-NCR area received an identical bomb threat by email early Wednesday, triggering mass evacuations and searches as panic-stricken parents rushed to pick up their children.

The threat was declared a hoax as "nothing objectionable" was found during searches, the police said.

According to the police officer, the email ID from which the threat was sent is 'sawariim@mail.ru'. Sawarim is an Arabic word extensively used by the terror outfit Islamic State (IS) in their propaganda videos over the past several years, the official said.

"Kill them wherever you meet and drive them out of the places from which they drove you. There are many explosive devices in the school...," reads the identical email sent to all schools.

The officer said that the email also contained "aayate (verses) of the holy Quran".

The investigators are looking into the timing angle too as the country is in the midst of Lok Sabha elections, he said.

"The main agenda of sending such threat emails in bulk is to create panic and wage a cyber war by some terror group," an officer, who did not wish to be named, said.

"The domain of email ID sawariim@mail.ru has been traced to Russia and is suspected to have been formed with the help of the dark web, which is an encrypted online content that allows individuals to hide their identity and location from others," he said.

After the threat received by the schools on Wednesday, buildings were evacuated and students were sent back home. The Delhi Police said they received the calls from 131 schools in Delhi.

Another police officer said, "The culprits must have watched past instances where students had sent such bomb threat emails to their schools as a prank. We are looking into that angle also." The Special Cell will also investigate the case of a bomb threat to Delhi's Chaha Nehru Hospital received through an email on Tuesday, police said.

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