The League of Conservation Voters is spending more than $300,000 on television ads supporting Democratic Sen. Sherrod BrownSherrod Campbell BrownElection Countdown: Trump confident about midterms in Hill.TV interview | Kavanaugh controversy tests candidates | Sanders, Warren ponder if both can run | Super PACs spending big | Two states open general election voting Friday | Latest Senate polls Overnight Health Care: Senators target surprise medical bills | Group looks to allow Medicaid funds for substance abuse programs | FDA launches anti-vaping campaign for teens Bipartisan group wants to lift Medicaid restriction on substance abuse treatment MORE in Ohio.

The league said the ad would run for two weeks in Columbus, Ohio. A Republican source tracking the political ad market said the league had purchased more than $300,000 of airtime through April 7.

The ad touts Brown's support for the clean energy industry in Ohio and credits him with attracting the jobs, technology and manufacturing equipment that accompany clean energy projects.

"It's the future of manufacturing right here at home, rather than in China or in Mexico," says the narrator in the ad. "With Brown's plan, we'll make it in Ohio."

The ad — which doesn't explicitly encourage viewers to vote for Brown — appears to push back on a key charge by Brown's GOP opponent, state Treasurer Josh Mandel, who has accused Brown of being "one of the main D.C. politicians responsible for Ohio jobs moving to China." The nonpartisan PolitiFact Ohio deemed that accusation to be false.

Brown's reelection fight has attracted millions of dollars in attack ads from conservative outside groups, who have named him one of their top targets for 2012. Mandel is also being supported by Sen. Jim DeMint (R-S.C.), whose PAC recently gave the Club for Growth $500,000 to use to support Mandel and three other GOP candidates.

The League of Conservation Voters has also been active this cycle in opposing another senator with the last name Brown — Republican Scott Brown of Massachusetts. The group spent $1.8 million in October on an ad criticizing him for supporting continued tax breaks for oil companies.

The Hill rates the Ohio Senate race as leaning Democratic.

Watch the ad: