Robert Dear, the man who admitted to killing three people at a Planned Parenthood clinic in Colorado late last year, has been deemed mentally unfit to stand trial, according to US media reports.

Judge Gilbert Martinez ruled on Wednesday that the 57-year-old must undergo psychiatric treatment before his criminal trial can continue.

As he was escorted out of the courtroom, the defendant called Martinez a "filthy animal," according to the Associated Press.

Dear is being tried on 179 criminal charges, including murder and attempted murder, after he allegedly attacked a women's health clinic in Colorado Springs on November 27. His rampage left three dead and nine injured after a five-hour standoff with police.

'Warrior for the babies'

The suspect has called himself a "warrior for the babies" in court and professed anti-abortion views.

Dear told the press via phone calls from jail that he suspects his lawyers of being part of a plot to downplay his pro-life message.

Martinez originally ordered the competency test after the defendant expressed a wish to fire his state-assigned attorney and represent himself in court.

State prosecutors disagreed with the judge's ruling, saying Dear's courtroom outbursts prove he understands what he has done and the proceedings against him.

Abortion remains a volatile subject in the United States, and attacks on providers are not unheard of.