More than 25,000 ballots remain uncounted in Alaska’s GOP Senate primary between Joe Miller (left) and Lisa Murkowski (right).

(CNN) – One day before vote counting resumes in Alaska's Republican Senate primary, election officials say more than 25,000 ballots remain uncounted.

According to unofficial results from last Tuesday's primary, Sen. Lisa Murkowski trails attorney Joe Miller by 1,668 votes, in what could turn out to be the biggest upset so far this cycle. Absentee ballots had 10 days domestically and 15 days internationally to arrive through the mail as long as they were postmarked August 24th, the day of the primary.

Officials at the Alaska Division of Elections tell CNN that as of Sunday 15,720 absentee ballots have been returned. Absentee ballots continue to arrive by mail. Also waiting to be counted are 663 early votes, ballots which were cast in pre-primary day voting. Add to that 9,117 "questioned" ballots, which may or may not be counted. Some may be disqualified by a panel of election officials for irregularities. Most of these votes are expected to be cast in the Republican primary, but some may be intended for the Democratic contest.

Election officials say they will determine Monday how many votes will be included in Tuesday's initial count.

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