The alleged Port Authority bomber spent an hour spilling his guts to investigators at Bellevue Hospital on Monday — saying he picked the specific hallway because of Christmas posters and that he was avenging violence against Muslims around the world, law enforcement sources said.

Akayed Ullah mentioned President Trump and past administrations during the grilling, and said his anger was fueled by decades of anti-Muslim bloodshed in Gaza, Syria and Iraq.

Ullah, a Bangladeshi immigrant, said the attack was specifically inspired by ISIS — “not al Qaeda” — and also mentioned seeing Christmas posters before detonating the device in the underground tunnel between the bustling bus depot and the Times Square subway.

The seasonal imagery set him off — inspiring him to follow ISIS Christmas threats, NBC reports.

ISIS propaganda released just weeks ago features a picture of Santa Claus in Times Square next to explosives and the phrase “We meet at Christmas in New York . . . soon,” according to terror watchdog group Site Intel.

An Islamic State militant also drove a truck into a Berlin Christmas market last year, killing 12 and injuring 56.

“He acknowledges he purposely set it off then and there,” a senior law enforcement official said.

He says he acted alone, building his crudely constructed bomb from commercially available parts based on instructions he found online, sources said.

Fortunately, the homemade pipe bomb didn’t detonate properly — and only wounded the wannabe suicide bomber and those around him.

Ullah was allowed to stop several times to pray during the interview, and was later taken to the intensive care unit for treatment of internal injuries suffered in the blast, sources said.