HONG KONG, June 21 (Reuters) - Hong Kong pro-democracy newspaper Apple Daily will be forced to shut "in a matter of days" after authorities froze the company's assets under a new national security law, an adviser to jailed tycoon Jimmy Lai told Reuters on Monday.

Mark Simon, speaking by phone from the United States, said the company has no more access to funds and it plans to hold a board meeting on Monday to discuss how to move forward. (Reporting by Anne Marie Roantree; Editing by Christopher Cushing)