Outside Democratic and Republican political groups spent more than $8.1 million combined over the last three months to promote or attack candidates in the weeks leading up to the Nov. 6 election for the 12th and 13th U.S. House district seats.

The vast majority of the outside money in both races was spent on attack ads, according to the most recent Federal Election Commission reports.

Both district races rank as two of the most closely watched House contests in the nation, with both major parties acknowledging that their hopes for controlling the legislative chamber rest upon success in Illinois.

Independent groups, such as charitable nonprofits or political action committees, are free to spend unlimited amounts of money to support or criticize federal candidates as long the groups do not coordinate with the candidates' campaigns, according to a 2010 U.S. Supreme Court ruling.

In the 12th U.S. House District contest, Republican groups -- primarily the National Republican Congressional Committee -- spent nearly $1.9 million on attack ads against Democratic nominee Bill Enyart, a Belleville attorney and former Illinois National Guard commander. Nearly $700,000 of that has been spent over the last three weeks, the FEC reports show.

The Democratic Congressional Campaign Committee so far has spent $1.67 million on attack ads against GOP nominee Jason Plummer, a Fairview Heights real estate developer, with nearly $1.2 million being spent over the last three weeks, the FEC numbers shows.

Philip Lesseigne, a Plummer campaign spokesman, said the large amounts of money the DCCC is spending against Plummer shows "how desperate they are and that their message is not working."

Jason Bresler, Enyart's campaign manager, echoed the same theme about Republicans, saying the large sums the NRCC must spend on anti-Enyart attack ads shows "their message is not working..."

Enyart and Plummer, along with Green Party nominee Paula Bradshaw of Carbondale, are seeking to replace U.S. Rep. Jerry Costello, D-Belleville, who is retiring after 24 years.

In the 13th House District race, Republican groups have spent nearly $2.4 million to defeat Democratic nominee Dr. David Gill, of Bloomington. The DCCC has spent more than $2.2 million to defeat GOP nominee Rodney Davis, of Taylorville.

Patrick Pfingsten, the Davis campaign spokesman, said it's "important to know Rodney Davis is the only candidate in this race who will stop taxes from increasing on all Americans, will help create an environment in which small businesses can thrive, and will repeal and replace Obamacare."

The Gill campaign did not return several calls seeking comment.

Katie Prill, a NRCC spokeswoman, said her group is spending the amount it has on attack ads against Gill because "Obviously, these are very competitive seats. We have two great candidates with Jason Plummer and Rodney Davis down there, that are really reaching out to voters and voters are liking the message they are hearing...Anything that we can do to get our message across is our goal."

Gill and Davis, along with independent candidate John Hartman, are seeking to replace U.S. Rep. Tim Johnson, R-Champaign, who is retiring after 10 years in office.