Lucknow, Dec 4 (IANS): The Uttar Pradesh Raj Bhawan has received a letter threatening to blow up the building if Governor Anandiben Patel does not vacate it in 10 days.

The letter, according to Raj Bhawan sources was sent by "TSPC Jharkhand", an apparent reference to the Maoist group Tritya Sammelan Prastuti Committee.

An FIR under the charges of criminal intimidation and threatening Governor/President under IPC Section 124 has been lodged with Hazratganj police station.

According to Hemant Rao, Additional Chief Secretary to Governor, the letter has been sent to the state home department for further action.

Additional Chief Secretary (Home) Avanish Awasthi said late on Tuesday night that the home department has taken the matter very seriously and written to DGP and DG Intelligence and ADG Security to investigate immediately and submit report by Wednesday after a full assessment of the situation.

Police sources said TSPC is suspected to be an offshoot of a Naxal group active in Jharkhand.

"The police are trying to find out the place from where the letter was sent. Meanwhile, security of the Governor and the Raj Bhawan is being beefed up further," said a government spokesman.