LITTLE ROCK, Ark. — Democratic U.S. Sen. Mark Pryor began running a re-election campaign ad Tuesday blaming the Republican looking to unseat him in next year's race, U.S. Rep. Tom Cotton, for helping cause the 16-day partial shutdown of the federal government that cost the country billions of dollars.

The 30-second television ad criticizes Cotton for backing House Republicans' efforts to tie federal spending bills to the defunding of the federal health care law. That push led to the standoff that shut down the government, which was re-opened by legislation last week that also raised the nation's borrowing limit.

"Cotton and a small group of reckless congressmen took our country to the brink of default. His irresponsible actions weakened our credit and damaged our economy," the ad's narrators say. "Fortunately, wiser heads prevailed. Senators like Mark Pryor brought Democrats and Republicans together to end the shutdown and responsibly cut spending."

The ad cites Standard & Poor's estimate that the shutdown cost the nation's economy $24 billion.

The spot highlights Pryor's work with a group of 13 other lawmakers tasked with ending the shutdown. It is the latest effort by the two-term senator's campaign to tie Cotton to the shutdown that has hurt Republicans nationally in the polls. The two have been engaged in an expensive TV ad war that has included spots from outside groups such as the Senate Majority PAC and the Club for Growth.

Pryor's campaign didn't say how much air time it had bought for the spot, but records show it bought more than $63,000 worth of air time on five Little Rock TV stations to run the spot through Nov. 1. Pryor's campaign said the spot was running statewide.

Cotton's campaign criticized the ad and noted the congressman's support for House-backed proposals to end the shutdown that sought other concessions on the health care law. Cotton's campaign said the computer bugs that have marred the rollout of the online insurance marketplace are a sign that Pryor should have backed the Republican efforts to extract one of those concessions: a delay in the law's implementation.

"We can see pretty clearly now with the debacle the rollout has been that the delay for individuals and families is badly needed," Cotton campaign manager Justin Brasell said. "Yet once again, Senator Pryor chooses partisan politics in Washington over the needs of people in Arkansas."

Cotton was elected in November to south Arkansas' 4th Congressional District, and announced in August he was challenging Pryor. Republicans have called Pryor, who was first elected in 2002, the most vulnerable Senate incumbent running next year.