A high school student from Wisconsin killed his parents as part of a larger plot to assassinate US President Donald Trump, the FBI has said.

Nikita Casap, 17, has been charged with the killing of his mother, Tatiana Casap, 35, and his stepfather Donald Mayer, 51, who were found dead at their home on 28 February.

A newly unsealed search warrant also alleges that the suspect's phone contained material relating to a neo-Nazi group called the Order of Nine Angles and praise for Adolf Hitler.

Investigators also discovered antisemitic writings in which the accused allegedly detailed his plans to kill Trump as a part of a broader goal to overthrow the government, according to the court document.

The suspect is accused of first-degree intentional homicide and seven other felony counts, including hiding a corpse and identity theft.

The parents were found dead when local officials visited their home in the village of Waukesha, near Milwaukee, after the boy failed to attend school for two weeks.

Mr Mayer had died from a gunshot wound to the head, while Ms Casap died from multiple gunshot wounds on or about 11 February, according to a criminal complaint concerning the teenager.

The same day their bodies were discovered, the defendant was pulled over by police in the state of Kansas while driving a 2018 Volkswagen Atlas belonging to Mr Mayer, investigators said.

In the car was Mr Mayer's Smith & Wesson .357 pistol, four credit cards belonging to the couple, "multiple pieces" of valuable jewelry, a pried-open safe and $14,000 (£10,700) in currency, most of which was inside a Bible, said the criminal complaint.

In writings found by investigators, the suspect expressed white supremacist beliefs and called for Trump's assassination to start a political revolution, according to the search warrant.

The alleged double murder "appeared to be an effort to obtain the financial means and autonomy necessary to carrying out his plan", investigators wrote.

The court documents allege the suspect was speaking with people in Russia about plans to kill his parents.

Authorities said the teenager paid for a drone and explosives to use in an attack - and had plans to escape to Ukraine.

"He was in touch with other parties about his plan to kill the president and overthrow the government of the Unites States," investigators wrote.

The suspect had a preliminary court hearing on 9 April. He has not entered a plea to the charges.

He is next due to appear in court for an arraignment - where he will be formally given the charges against him - on 7 May, according to the Waukesha County Court. He is being held on a $1m (£764,000) bond.