BELFAST, Northern Ireland - Police, and politicians in Northern Ireland appealed for calm on Monday after a third night of violence that saw Protestant youths start fires and pelt officers with bricks and gasoline bombs.

The flareups come amid rising tensions over post-Brexit trade rules for Northern Ireland and worsening relations between the parties in the Protestant-Catholic power-sharing Belfast government.

The Police Service of Northern Ireland said officers were attacked in Londonderry on Sunday night, and there was also unrest in two pro-British unionist areas near Belfast. Police said most of those involved were teenagers.

Chief Superintendent Darrin Jones condemned the "senseless and reckless criminal behavior that (does) nothing but cause damage to the community."

The disturbances followed unrest Friday and Saturday in unionist areas in and around Belfast and Londonderry, also known as Derry, that saw cars set on fire and projectiles and gasoline bombs hurled at police officers. Police said 27 officers were injured, and eight people have been charged, the youngest a boy of 13.

Britain's economic split from the European Union at the end of 2020 has shaken the delicate political balance in Northern Ireland, a part of the U.K. where some people identify as British and some as Irish.

A new U.K.-EU trade deal has imposed customs and border checks on some goods moving between Northern Ireland and the rest of the U.K. The arrangement was designed to avoid checks between Northern Ireland and Ireland, an EU member, because an open Irish border has helped underpin the peace process built on the 1998 Good Friday accord.

The accord ended decades of violence involving Irish republicans, British loyalists and U.K. armed forces in which more than 3,000 people died. But unionists say the new checks amount to a new border in the Irish Sea between Northern Ireland and the rest of the U.K.

The Democratic Unionist Party, which jointly governs Northern Ireland with Irish nationalist party Sinn Fein, has called for the Brexit deal to be scrapped.

Unionists are also angry at a police decision not to prosecute Sinn Fein politicians who attended the funeral of a former Irish Republican Army commander in June. The funeral of Bobby Storey drew a large crowd, despite coronavirus rules barring mass gatherings.

The main unionist parties have demanded the resignation of Northern Ireland's police chief over the controversy, claiming he has lost the confidence of their community.

Mark Lindsay, chairman of the Police Federation of Northern Ireland, said the "political atmosphere" was being used as an excuse for violence, orchestrated by banned paramilitary groups.

"Older, more sinister, elements use the youth and use children...to achieve their aims," Lindsay told BBC radio.