Sen. Mark Pryor launched a new campaign ad Tuesday declaring his Republican opponent in the Arkansas Senate race, Rep. Tom Cotton, "reckless and irresponsible."

Pryor was responding to an ad Cotton began running Monday in which he accuses the Democratic senator of supporting a government funding measure that also protected the unpopular Obamacare. Pryor called Cotton's charge "silly."

Pryor also hits Cotton for focusing on politics in the middle of a government shutdown and dings the Republican for missing votes during the government funding debate.

"Tom Cotton: just reckless and irresponsible," the ad's narrator says.

The dueling ads — the first in what is expected to be one of the most competitive Senate races of 2014 — are an indication of how hard the two sides intend to fight for a long-time Democratic seat Republicans need to win if they're to secure control of the Senate.

The race has already attracted interest from outside groups as well. The conservative Club For Growth, which has endorsed Cotton, on Tuesday announced a six-figure investment in a new anti-Pryor television ad.