South Korea's state election agency said Wednesday it has asked the prosecution to investigate allegations that illegal campaign text messages had been sent to voters after official campaigning came to an end.

The ruling Saenuri Party had earlier claimed that the messages, which urged people to vote for the main opposition Democratic United Party's candidate, Moon Jae-in, were sent in large numbers after official campaigning closed at midnight Tuesday.

The DUP later acknowledged that the party sent the messages, but insisted that no law was broken because it sent the messages around 10 p.m. Tuesday and their arrivals appear to have been delayed due to mobile traffic problems.

The watchdog National Election Commission referred the case to the prosecution.

Campaigning on Election Day is a crime punishable by prison terms.

The race has been a dead heat between Park Geun-hye of the conservative ruling Saenuri Party and her main opposition rival Moon. Many pre-election surveys have shown the two running neck-and-neck within the margin of error.

Public interest is high for the election, which is expected to be one of the tightest ever. Voters stood in long lines at polling stations despite a cold wave that pulled down temperatures to as low as minus 10.3 degrees Celsius in Seoul.

Seven hours after the polls opened at 6 a.m., election officials reported an average voter turnout of 45.3 percent nationwide as of 1 p.m., higher than 36.7 percent and 41.9 percent reported at the same time in the previous presidential votes in 2007 and 2002, respectively.

The polls are scheduled to close at 6 p.m.

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文측"투표 독려 문자 어제 보낸 것이 지연"

민주통합당 문재인 대선후보 측은 19일 문 후보 지지를 호소하는 내용의 문자 메시지가 공식 선거운동 기간 이후에도 발송돼 불법이라는 새누리당의 주장에 대해 "법적으로 아무 문제가 없다"고 반박했다.

박광온 선대위 대변인은 이날 영등포 당사 브리핑에서 "어젯밤 10시3분에 투표를 독려하는 내용의 문자 메시지를 20개씩 끊어보내는 수동발신으로 보냈다"며 "일부 메시지가 오늘 아침에 도착한 것은 트래픽에 걸려 늦게 도착한 것"이라고 말했다.

그는 "문자를 보낸다 하더라도 통신회사를 거쳐 가야하기 때문에 지연발송된 것으로 확인됐다"며 "합법, 불법의 문제는 발신 시간이 기준이어서 자정을 넘어서 발신했느냐를 놓고 판단해야 한다"고 강조했다.

그는 새누리당이 당선무효를 거론한 것에 대해 "투표율이 높아 스스로 패색이 짙어지고 있음을 인정하는 것"이라며 "마지막 순간까지 투표율을 떨어뜨리려는 불순한 의도를 숨기지 않아 실망스럽다"고 비판했다.