This sounds more like a headline than a sentence.
I'd suggest inserting an "a" and changing the grammar a bit.
FROM:
Turkey declares three-month state of emergency.
TO:
Turkey has declared a three-month state of emergency.
Or, change it to past tense and add a date, so it becomes a sentence that states a historical fact. Perhaps this would mean the sentence might be more useful a few years from now and not just today and in the near future.