Sen. Scott Brown (R-Mass.) today said White House contender and former Massachusetts Gov. Mitt Romney, his close political ally, is in “a different world” than Brown when it comes to money.

“Listen, he’s in a category, a lot of those folks are in categories that we don’t really understand,” Brown said on the “Jim and Margery” talk-radio show this morning. “And certainly he has to release his [tax] returns. I understand he’s going to do that like everybody else when they become ready and available in April. I don’t know anything [about] his finances. I really — it’s kind of a different world for me.”

Romney, who has not yet released his tax returns, was tweaked by his GOP opponents in recent TV debates over the issue.

Brown and Romney share GOP strategist Eric Fehrnstrom as a key political adviser.

Brown officially launched his re-election campaign in Worcester, Mass., Thursday night, emphasizing that he would continue to be an independent voice for the Bay State.

“I’m not going to have the political establishment behind me,” he said two years after his upset special election victory. “All I’m going to have going for me is my independent record as your United States Senator and the independent spirit of you, the Massachusetts voter,” Brown said to applause.

According to a new CQ Vote Study, Brown voted with Republicans only 54 percent of the time in 2011 in votes where a majority of Republicans voted against a majority of Democrats.

In 2010, a majority of registered voters in the Bay State were not affiliated with either party.

Brown faces presumptive Democratic nominee Elizabeth Warren, a Harvard professor. Warren, in an attempt at counter-programming, arranged a so-called moneybomb Thursday. Her campaign pulled in $1.2 million in 24 hours.