As for your comment that "This article defines what is a security area.", you will also note that Section 48(1) states that "if he considers it to be necessary for the purpose of suppressing such organised violence, proclaim such area as a security area for the purposes of this Part".
Hence the precursor to anything relating to a security area under the ISA is that a proclaimation must first be made.
Lets also revisit Section 48(3) and (4) of the ISA:
s48(3) A proclamation made under subsection (1) shall be published in such manner as the Minister thinks necessary for bringing it to the notice of all persons who in his opinion ought to have notice thereof and shall have effect as soon as such notice has been given, without publication in the Gazette.
s48(4) A copy of every proclamation made under subsection (1) shall be published in the Gazette and shall be presented to Parliament as soon as possible after it has been made.
The proclaimation must be made in accordance with s48(3) and later published in the Gazette and presented to Parliament in s48(4). I doubt that press statements ALONE will satisfy both s48(3) and (4).
I'm not sure about your hypothetical situation, but that's how the ISA seems to work. Perhaps the security area can be the whole of Singapore, but still, the proper method of proclaimation must happen before it is designated as a security area.
Originally Posted by zaren