DENVER -- Denver police say they found rocks, bricks and sticks stashed around the city during the Democratic National Convention that may have been placed there by people planning violence.

Police spokesman John White said Tuesday the discovery and confiscation of the objects may have helped officers keep last week's convention relatively peaceful. He declined to give details of the discoveries, such as when police found them or where the items were left.

Authorities say 152 people were arrested during a six-day period leading up to and including the convention.

By contrast, 286 people were arrested on Monday alone during an anti-war demonstration in St. Paul, Minn., where Republicans are meeting this week. Authorities say a few of the 10,000 protesters broke windows, slashed tires and harassed delegates.

During the week leading up to the convention, police were sent a memo that warned them to be on the lookout for stockpiles of protester supplies, ranging from pipes to bikes.