Colombo: Sri Lankan authori­ties have stepped up the security of President Maithripala Sirisena following an alleged plot to assassinate him, presid­en­tial officials said on Thursday. “People in charge have taken measures to strengthen his security. Certainly his security has been beefed up,” Shiral Lakthialaka, one of the presid­e­n­tial advisers, said. On the probe about the alleged plot to assassinate the President, he said political attempts are being made to undermine the credibi­lity of the investigation by questioning the conduct of the man who had bared the plot. “There is a concerted effort to undermine the investigation. This could be a political conspiracy,” he said.