PHOENIX (AP) — The Latest on the U.S. Senate race in Arizona (all times local):

9:40 p.m.

Republican party officials are suing to limit what ballots can be counted in the slow-motion tally of Arizona's nail-biter of a Senate race.

County officials were still counting more than 600,000 ballots when four local Republican parties filed the lawsuit Wednesday night. It challenges the way counties have allowed voters to fix problems with signatures on mailed-in early ballots.

The complaint singles out the state's two biggest urban counties, which are the base of Democratic Rep. Kyrsten Sinema's support. She and Republican Rep. Martha McSally are separated by only a few thousand votes. Counting the outstanding votes could take several days.

The lawsuit asks a judge to prevent the county officials from counting certain ballots that were delivered with signature issues. It's unclear how many of those ballots exist.

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1:30 p.m.

Arizona's nationally-watched and incredibly tight Senate race between Republican Martha McSally and Democrat Kristin Sinema may not have a declared winner until Thursday or even next week because, ironically, the state's voters like to cast their ballots early.

About three-quarters of Arizona voters cast ballots by mail. But many ballots known as "late earlies" arrive in the mail on Election Day, in the few days leading up to it or are hand delivered by the voters themselves. Those ballots can create logjams at the state's 15 county recorders' offices where vote counting is conducted.

All mailed ballots and the ballots that could have been mailed but were dropped off by the voters require a series of labor-intensive verifications. Voter signatures on the envelopes containing the ballots must be verified before the votes are tabulated.

McSally and Sinema were separated Wednesday by a small fraction of the tabulated votes, with hundreds of thousands of uncounted ballots still outstanding. More than 600,000 votes were uncounted in a race where more than 2 million people cast ballots.