Hi,
'No comment' is the standard remark made by someone who is being asked questions by the press and doesn't want to say anything. 'No comments' would be used in a fuller statement as in: I have no comments to make on the situation. As a question it would be: Have you any comments you would like to make on the present crisis? In other words the use of 'comment' in the plural is when you are asking or replying in a complete sentence.