An email was sent to the schools on Monday night.
Just a day after an explosion occurred outside a Central Reserve Police Force (CRPF) school in Delhi, all such schools across the country received an email threatening that they would be bombed, sources said.
Officials said the email, sent on Monday night, threatened explosions at all CRPF schools by 11 am on Tuesday. An investigation began immediately and the threat was found to be a hoax.
Delhi has two such schools, in Rohini and Dwarka. An explosion had ripped through the wall of the school in Rohini's Prashant Vihar on Sunday morning and several shops and vehicles had also been damaged. No one had been injured.
The explosion is being investigated by the National Investigation Agency, the CRPF and the National Security Guard. A case has also been registered by the Delhi police.
The hoax threat against CRPF schools comes at a time when similar threats have been issued against over 100 flights since October 14. Reports said 30 flights received such threats on Monday night and another 10 on Tuesday.
Union Civil Aviation Minister Ram Mohan Naidu has said safety is the government's top priority and rules are being amended to put people who make such calls on the no-fly list.