Two major polls released Sunday showed Republicans solidifying a slight edge in the battleground races that will determine control of the Senate.

Both a new NBC News/Marist poll and a New York Times/CBS News/YouGov survey suggest that the GOP holds narrow but increasingly stable leads in enough swing states to give them a slight majority in the Senate if the results hold up through the midterm elections nine days away.

The Marist polls of six key states released Sunday show the GOP picking up momentum and maintaining tight leads in four of the races. In another race, South Dakota, the Republican candidate Mike Rounds has moved into a 14-percentage-point lead, outside the margin of error.

In the last state, North Carolina, Democratic Sen. Kay Hagan's lead over Republican Thom Tillis has shrunk to a tie, with each candidate drawing 43 percent. Most recent polls have shown Hagan with a slight lead.

In other states where Democrats hoped to pick up a GOP-held seat, the odds have moved away from the Democratic candidates.

The chaotic Kansas election between incumbent Republican Pat Roberts and independent Greg Orman has shifted in Roberts' direction, according to both the Marist and YouGov polls. Roberts has moved from a tie two weeks ago to a four-percentage-point lead in the YouGov poll, and from a 10-point deficit to a dead heat in the Marist poll.

In Georgia, Republican nominee David Perdue has a narrow three-percentage-point over Democrat Michelle Nunn in a race that has been extremely close in other polls.

In Colorado and Iowa, two swing states the Democrats must hold to retain control of the Senate, the races remain dead heats.

Incumbent Sen. Mark Udall leads GOP challenger Rep. Cory Gardner by one point in the YouGov poll, but trails by one point in the Marist poll.

In the race for Iowa's open seat, Republican Joni Ernst has a three-point lead over Democrat Bruce Braley by Marist's tabulation, but is tied with him at 44 percent in the YouGov survey.

Republican candidates continue to hold small but stable leads in Arkansas, Kentucky, Alaska and Louisiana.

The NBC/Marist polls were conducted between Oct. 18 and 23, reaching over 600 voters in each state. The New York Times/CBS News/YouGov survey polled more than 80,000 respondents in online interviews.