Dhaka, April 25 -- Authorities have ordered heightened security across Bangladesh after the Police Headquarters warned that a banned "extremist organisation" could target parliament and other critical installations.

A directive issued on Thursday instructed all police units to tighten vigilance and increase surveillance.

The communication does not name any specific organisation, but refers to the recent arrest of a man identified as Istiaq Ahmed Sami, also known by several aliases including Abu Bakr and Abu Muhammad.

It does not specify when or by which unit the arrest was carried out.

It warns of possible attacks involving explosives, locally made bladed weapons, and firearms, and outlines a range of potential targets including state...