Democratic candidate Rick Weiland looks around the studio before a televised U.S. Senate candidate debate Oct. 23 at the South Dakota Public Broadcasting studio in Vermillion, S.D. (Elisha Page/Argus Leader via AP)

South Dakota Democratic Senate nominee Rick Weiland has accused national Democrats of working against him and trying to quietly boost independent Senate candidate Larry Pressler, a sign of intra-party discord rarely seen this close to Election Day in a key race.

Weiland says the Democratic Senatorial Campaign Committee's ad attacking Republican Mike Rounds, the frontrunner in the race, will also hurt him.

"They have been less than honest, I think, about their intentions," Pressler Weiland told The Washington Post. "They come in here and they spend a bunch of money on this negative attack on Rounds with their disclaimer," he said, adding that the "only one who is going to benefit" is Pressler.

Weiland made similar remarks at a news conference earlier Monday.

The DSCC has released an ad slamming Rounds over an immigration investment scandal that has dogged him in the campaign. The scandal dates back to Rounds's tenure as governor and involves members of his administration.

When asked for the DSCC's reaction to Weiland's comments, spokesman Justin Barasky declined to comment.

The DSCC announced this month that it was launching a $1 million campaign to save the seat of retiring Sen. Tim Johnson (D). At that point, polls showed a competitive contest between Weiland, Rounds and Pressler.

But in recent weeks, amid spending reinforcements from the National Republican Senatorial Committee, Rounds has appeared to regain the advantage he held for most of the year. An NBC News/Marist poll released Sunday shows Rounds leading Weiland 43 percent to 29 percent, with Pressler lagging behind at 16 percent.

National Republicans have hit the air with an ad attacking both Weiland and Pressler as too liberal for the state. Pressler is a former Republican senator who is not saying which party he would caucus with if the majority comes down to him.

This is not the first time tension between Weiland and Senate Democrats has flared up publicly. Senate Majority Leader Harry M. Reid (D-Nev.) said of Weiland last year, “He’s not my choice." Weiland said in a debate last week that he opposes Reid continuing to serve as the Democratic Senate leader.

But Democratic Senatorial Campaign Committee executive director Guy Cecil told Bloomberg Politics last week, "we want Weiland to win."

Updated at 6:01 p.m.