A trial helicopter landing at the site (left) in Mathura, where PM Narendra Modi is scheduled to hold a rally on Monday

An unidentified person or organisation has threatened to assassinate Prime Minister Narendra Modi during his slated visit to Deendayal Dham in village Nagla Chandrabhan on May 25.

While there were already intelligence inputs that PM Modi might be targeted by terrorist groups during his visit to Deendayal Upadhyay's village, Mathura Senior Superintendent of Police Rakesh Kumar on Saturday received a threat letter and also an SMS on his mobile.

Although he didn't reveal the content of the letter and the message, he confirmed to newspersons that it was about a conspiracy to blow up Modi's dais during his rally in the village.

Superintendent of Police (Crime) Ashok Kumar Rai said, "We have received a letter and a mobile message. The police are at work and trying to find out the origin of the letter and the message, and the person or the organisation behind it."

The police have enhanced the security in the village and the areas through which PM Modi would pass during his over two-hour stay. Five helipads have been constructed; the entire area has been barricaded.

"There is a three-tier security arrangement for the prime minister. The intelligence units of the Army and the Central government would also be active there. We have already started our exercise and keeping an eye on every person," SSP Rakesh Kumar said.

Meanwhile, sources in the police department told Mail Today that the Special Protection Group (SPG) has expressed its dissatisfaction over the security measures of the state police in the village.

"Over 30 SPG men led by DIG Alok Gupta were here on Friday and Saturday and pointed out over a dozen lapses. Then they handed over a blueprint of the security arrangement to the state police. They expect everything should be in place by Sunday morning," an officer said.

After this review, the state government has decided to deploy 10 companies of the Provincial Armed Constabulary (PAC) and five companies of Rapid Action Force (RAF). Earlier, the plan was to deploy eight PAC and two RAF companies. The initial plan was to erect 16 Door Frame Metal Detector gates which would now be increased to 30 by Sunday. Previously, there were 150 Local Intelligence Unit (LIU) personnel on duty. But 100 more LIU men would be there a day before Modi's programme.

Fifteen IPS officers and 50 officers of additional SP rank would be on duty from the evening of May 24. The Anti Terrorist Squad and National Investigation Agency have also deployed their personnel in civil dresses.

"Gupta has sought an NOC from Anil Kumar, Executive Engineer of Public Works Department (PWD), about the helipads. As per our reports, there are 42 sleeping modules of the terrorist groups in western Uttar Pradesh who may be active at the moment", the officer said.