Four hospitals in Delhi -- Deep Chand Bandhu Hospital, GTB Hospital, Dada Dev Hospital, Hedgewar Hospital -- have received a bomb threat via email. Officials said that nothing suspicious was found following a search operation.

Meanwhile, the Delhi Police have initiated a probe to trace the origin of the threat mail.

As soon as information was released, a bomb disposal squad, bomb detection team, fire department and local police rushed to the spot to conduct searches, PTI news agency quoted the officials as saying.

According to a Delhi Fire Services official, the spate of calls regarding the bomb threat mails began at around 10.45 am.

Deep Chand Bandhu Hospital in Ashok Vihar received the first call at 9.45 am, Dada Dev Hospital in Dabri at 10.55 am,Hedgewar Hospital in Farsh Bazar at 11.01 am and GTB Hospital in Shahdara at 11.12 am.

"Police and the bomb disposal squad are conducting the checks. We have also conducted checks twice. Nothing suspicious has been found so far," said V K Sharma, security officer at Hedgewar Hospital.

The mail about an explosive in the hospital was received by a doctor at the hospital, he said.

On Sunday, 20 hospitals in Delhi and the Indira Gandhi International Airport received bomb threats via emails. Delhi Police dismissed the threat as a hoax.

On May 1, bomb threats were sent to more than 150 schools in Delhi-NCR, which later turned out to be a hoax.

The threats were sent to the schools using a Russian email service.

Delhi Public School's (DPS) Dwarka and Vasant Kunj units, Mother Mary's School in East Mayur Vihar, Sanskriti School, Amity School in Pushp Vihar and DAV School in South West Delhi were among the 100 schools that received the threat.

In Noida, DPS and Apeejay School also received similar threats.