Thiruvananthapuram: The Kerala police have registered a case after BJP chief K Surendran received a purported threat letter. The source of the letter is currently untraceable, but it contains a threat to attack Prime Minister Narendra Modi during his two-day Kerala visit, scheduled for April 24.

The intelligence bureau (IB) report related to PM Modi's Kerala visit has reportedly taken note of the letter and has directed concerned authorities to maintain vigilance and ensure security.

There are reports of international terrorist organizations and their suspected sleeper cells in the state, as well as the apparent presence of Maoist groups, the ban of the Popular Front of India (PFI), and the alleged extremist tendencies of the Peoples Democratic Party (PDP) and Welfare Party of India posing a potential threat to security during the Prime Minister's visit.

During his visit, PM Modi is set to flag-off Kerala's first Vande Bharat Express train and inaugurate the Kochi Water Metro.