WASHINGTON (AP) — WASHINGTON (AP) — Supreme Court justices seem conflicted on whether they think states can force people to prove their U.S. citizenship before registering to vote.

Arizona is challenging a lower court's refusal to let it demand that prospective voters document their U.S. citizenship in order to use a federal registration form that doesn't require such proof.

A federal appeals court threw out that part of Arizona's Proposition 200, which was passed to stop illegal immigrants and other noncitizens from registering.

Several justices questioned whether the state can require information that the federal government did not require for federal voter registration. But others questioned whether the government's only requirement that someone swear that they're a citizen was enough.

A decision will come later this year.