A Florida man who plotted to blow up a synagogue and Jewish school during Passover last year will be hospitalised for psychiatric treatment and likely serve a maximum of 25 years in prison.

Muslim convert James Medina, 41, was handed the sentence by a Miami federal judge on Tuesday (28 November) after pleading guilty to a religious hate crime and attempting to use a weapon of mass destruction.

Authorities said Medina planned to attack the Aventura Turnberry Jewish Center in Hollywood, on Florida's east coast. The complex includes a synagogue, school and meeting halls.

He was arrested in April 2016 after approaching the centre with a fake bomb provided by an undercover FBI informant following a sting operation.

The plot could have killed countless numbers of the centre's 800-strong congregation.

FBI recordings showed Medina supported the Islamic State terror group and claimed an obligation to attack Jews in the US.

His lawyers said he suffers from significant mental health problems, and has been diagnosed with a schizoaffective disorder.

After an agreement between the prosecution and defence, US District Judge Robert Scola ordered that Medina spend the first portion of his sentence in a federal prison medical ward, where he can receive treatment for mental illness and a brain cyst.

He will then be transferred to a general population section of a prison if or when he is deemed fully recovered.

Medina only spoke briefly during Tuesday's hearing.

"I just need help. I need help, Your Honor. You know I lost everything," Medina said, according to the Sun Sentinel. He added: "I lost my mind, I lashed out."

Medina, a US citizen, was raised Christian but said he converted to Islam after going through a difficult divorce.

Court records show he has a long history of mental illness and has previously been committed for treatment in psychiatric hospitals. A car crash led doctors to discover a brain cyst in 2007, which was said by some medical experts to have affected his behaviour and ability to make good decisions.

His plot to attack the Jewish centre was thwarted after a tipster, who has not been publicly identified, told agents Medina was planning to shoot people with AK-47-style assault rifles in a synagogue.

An undercover sting operation saw FBI agents steer Medina away from using guns on account of it being harder to control his access to weapons. They instead hatched the plan to provide him with a fake bomb.

According to the FBI, Medina wanted to create a leaflet to be left at the scene in which he would claim the attack was traced to Islamic State. There's no evidence the group was actually linked to Medina, but he told the informant that leaflet would "make it look like it's Isishere in America. Just like that".

He also allegedly told an undercover FBI informant he was prepared to kill women and children. He also allegedly made several videos before the planned attack on the synagogue, including one in which he said goodbye to his family, the Sun-Sentinel reported at the time.