New Delhi: Bomb threat emails to around 150 schools in Delhi-NC are suspected to have been sent from Budapest, Hungary earlier this month, Delhi Police officials said on Tuesday.

According to an official, the IP address of these emails has been traced to Budapest and Delhi Police will soon contact their counterpart in Hungary for further investigation.

An IP (Internet Protocol) address is a unique identification number assigned to every device connected to the Internet.

The mail, allegedly sent from the mail.ru server, claimed that explosives had been planted on the school premises, triggering mass evacuations and searches and panicked parents rushing to pick up their children on 1 May. Ran away.

The threat, which had set off alarm bells in the security establishment, was belatedly declared a hoax as nothing incriminating was found on the school premises.

After registering the FIR in the case, the police had written a letter to Russia-based mail service company 'mail.ru' through Interpol.

Police were investigating the IP address used to send the e-mail, besides the sender and the source of the mail, to understand the conspiracy and motive behind the bomb hoax which resulted in panic in Delhi-NCR on Wednesday.

Officials said preliminary investigation has suspected a "deep conspiracy" hatched by a terrorist group during the ongoing Lok Sabha elections, adding that the threat mail may have been sent by an ISIS module.