The Union government has upgraded the security cover of Assam Chief Minister Himanta Biswa Sarma to the top category of Z+ after a recent review, officials said on Friday. Himanta Biswa Sarma has been enjoying a Z category cover provided by the Central Reserve Police Force (CRPF) VIP security unit for his travel in the north eastern states till now. After a recent security review, the CRPF has been directed by the Ministry of Home Affairs (MHA) to upgrade his security to the top category of Z+ on an all-India basis, the officials said.