The US Supreme Court has been asked to weigh in on whether anti-abortion activists can display crude photographs of aborted fetuses during protests.

The conservative Thomas More Society has petitioned the apex court to overturn an order by a Colorado court banning the display of "gruesome images of mutilated fetuses or dead bodies" that might be viewed by children.

Two anti-abortion activists brandished the images alongside a religious procession on Palm Sunday in Denver, prompting the St John in the Wilderness church to seek an injunction to protect children forced to look at them.

In its Supreme Court filing, the Thomas More Society said the ban violated the free speech rights of "pro-life" activists who were seeking to counter the "invisible abstraction" of fetal life.

It likened the images of the fetuses to those of victims of the Holocaust or lynchings that make "visceral what one dares not imagine."

The Supreme Court is expected to decide in the coming weeks whether or not it will take up the case.

Separately, Oklahoma officials have asked the court to review a state law that limits the use of an abortion pill, RU-486, which a state judge ruled was unconstitutional.

Other cases dealing with abortion are expected to come before the court in the coming months as more states pass laws that place greater restrictions on the procedure, which has been legal in the United States for 40 years.

At the end of October 2012, the court refused to review its 1973 "Roe versus Wade" decision legalizing abortion, turning away a petition on an amendment to Oklahoma's state constitution that would have granted "personhood" to embryos.

Had the Supreme Court upheld the amendment it would have extended constitutional protections of life to all embryos, thereby effectively outlawing abortion.