OTTAWA (Reuters) - Canadian Prime Minister Justin Trudeau on Monday plans to invoke rarely used emergency measures to tackle ongoing protests that have shut border crossings, and also blocked the capital for more than two weeks, sources said.

       Separately, the prime minister's office said Trudeau would speak to reporters at 4:30 p.m. ET (2130 GMT) without specifying why.

       One of the sources, who could not speak on the record due to the sensitivity of the situation, said the aim of using the emergency powers was to provide federal police support to local and provincial forces, not to use the military.

       (Reporting by Steve Scherer; Editing by Chris Reese)