OTTAWA, Feb 15 (Reuters) - Ottawa's police chief resigned on Tuesday after criticism that he did not do enough to stop COVID-19 protests that have paralyzed Canada's capital city and forced Prime Minister Justin Trudeau to invoke emergency powers.

A trucker-led movement calling on the government to lift vaccine mandates has occupied parts of downtown Ottawa since late January and blocked U.S. border crossings, inspiring similar protests around the world even as Canada moves to lift some health restrictions.

Protesters retreated from the Ambassador Bridge to Detroit and two other crossings after threats of fines and jail time. But hundreds of trucks are still blocking downtown areas, raising questions over Ottawa Police Chief Peter Sloly's handling of the crisis.

Diane Deans, chair of the Ottawa police board, said the city had reached "mutually agreeable separation" with Sloly, without saying why he had stepped down.

Critics alleged he was too permissive toward protesters who at the peak of their movement had parked 4,000 trucks and vehicles near Canada's parliament, prime minister's office and other government buildings.

In a statement announcing his resignation, Sloly said he had done "everything possible to keep this city safe and put an end to this unprecedented and unforeseeable crisis." His defenders had voiced fears the use of force by police could stoke violence.

Trudeau sought on Monday to beef up policing by invoking the Emergencies Act, which empowers his government to cut off protesters' funding and reinforce provincial and local law enforcement with federal officers.