WARSAW, Poland (AP) — Polish officials have joined war veterans to pay tribute to a World War II-era underground force that collaborated with Nazi German forces for a time toward the end of the war in their battle against Communists imposing control on the nation.

A Mass in Warsaw on Sunday opened ceremonies honoring the Holy Cross Mountains Brigade of the National Armed Forces on the 75th anniversary of its formation.

President Andrzej Duda's official patronage and the presence of ruling party officials underlined the right-wing government's rehabilitation of a unit celebrated by the far right.

The ceremonies were criticized by children of Polish resistance fighters and Poland's chief rabbi, who rejected an invitation and called it "a personal insult."

Poland had a large underground Home Army that never collaborated with the Germans.