An FBI manhunt for a Philadelphia man accused of murdering his girlfriend is underway and "very active."

The FBI has listed Justin Smith, 23, of Greensboro, North Carolina, on its "most wanted" list and is assisting the Philadelphia Police Department in its search for the suspect accused of killing his 21-year-old girlfriend, Dianna Brice.

"Smith is wanted for murder in the death of his pregnant 21-year-old girlfriend, who disappeared on March 30, 2021, and whose body was found on April 5, 2021," the FBI's most-wanted report reads. "Smith is alleged to have shot the woman in the head multiple times, causing her death and the death of her unborn child."

Upper Darby, Pennsylvania, police first responded to a missing person report regarding Brice on March 30, when they met with the victim's mother, who told authorities that her daughter was last seen getting into Smith's gray Ford Fusion in Landsdown.

Upper Darby police then requested assistance from the Philadelphia Police Special Victims Unit and FBI Violent Crimes Task Force "fearing nefarious actions," authorities told Fox News in a statement.

PENNSYLVANIA MISSING PREGNANT WOMAN FOUND DEAD IN SOUTHWEST PHILLY

Police found Brice's pregnant body in a debris pile in Philadelphia on April 5.

The Philadelphia Medical Examiner's Office conducted an autopsy and noted the cause of death as "multiple gunshot wounds to the head" and ruled the manner of death as a homicide, according to police.

Police also arrested a 21-year-old female fugitive named Tylydiah Garnett on April 10 in connection with Brice's death. Charges against Garnett include arson, criminal conspiracy and abuse of a corpse. 

Garnett is accused of helping Smith dispose of Brice's body and burn his vehicle, according to Fox 29 Philadelphia.

Betty Cellini, Brice's mother, previously told the outlet that Brice and Smith had an argument before her disappearance and said her daughter had a 4-year-old son in addition to her other son on the way.

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"Words don't express how sad it is for a young woman who leaves behind a 4-year-old child and was three to four months pregnant with her second. Words don't explain how sad it is for her family," Upper Darby Police Superintendent Timothy Bernhardt said during an April 6 press conference, according to Fox 29.

The FBI is offering a monetary reward to anyone with information that could lead to Smith's arrest. The suspect is considered armed and dangerous, and authorities are describing the case as "very active" and under investigation. 

The agency is encouraging anyone with information related to Smith to contact their local FBI office or the nearest American Embassy or Consulate.