Riots broke out late Friday and early Saturday in some nationalist areas where many Catholics still hope for a united Ireland, The Times of London reported. Thirteen police officers were injured in Portadown, including four who were hospitalized, and another in Belfast.
An undetermined number of people were arrested.
Robert Saulters, the grand master of the Orange Order, used the anniversary to attack Sinn Fein, the major nationalist political party.
"It is sickening to us, following such dastardly attacks on our people for 35 years, to see the commanders of that enemy sitting in government today acting as politicians who care for the peaceful existence of the people," Saulters said at a speech in Dromara, County Down.
The speech was at odds with the order's effort to depict July 12 as OrangeFest, a cultural celebration open to all.