WASHINGTON — Sen. Susan Collins, R-Maine, on Sunday called the Internal Revenue Service’s singling out of conservative groups for extra scrutiny “absolutely chilling” and called on President Obama to condemn the effort.

“This is truly outrageous and it contributes to the profound distrust that the American people have in government,” Collins, a moderate Republican, said on CNN’s “State of the Union.” “It is absolutely chilling that the IRS was singling out conservative groups for extra review, and I think it’s very disappointing that the president hasn’t personally condemned this and spoken out.”

The IRS apologized Friday for flagging groups seeking tax-exempt status with “tea party” or “patriot” in their names for extra attention. The official who oversees tax-exempt groups at the agency said the effort was not motivated by partisanship. White House Press Secretary Jay Carney said Obama was “concerned” about the reported behavior “of a small number” of IRS employees.

“(Obama’s) spokesman has said it should be investigated, but the president needs to make crystal clear that this is totally unacceptable in America,” Collins said.

Rep. Mike Rogers, R-Mich., echoed Collins on “Fox News Sunday.” The House Intelligence Committee chairman called for an external investigation into the matter, with congressional oversight.

“This should send a chill up your spine. This is something we cannot let stand. It needs to have a full investigation,” Rogers said.

An inspector general’s report set to be released this week says IRS officials knew about the targeting of conservative groups as early as 2011, months before the agency’s commissioner told Congress it wasn’t taking place.

“I just don’t buy that this was a couple of rogue IRS employees,” Collins said. “After all, groups with ‘progressive’ in their names were not targeted similarly. There is the evidence that higher level supervisors were aware of this. And the IRS was not forthcoming in telling Congress about the problem.”

Rep. Adam Smith, D-Wash., adopted a different tone. He said on “Fox News Sunday” the matter is “definitely worth looking into,” but made clear that he is “not going to leap to conclusions based on initial reports.” Sen. Dianne Feinstein, D-Calif., said on NBC News’s “Meet The Press” that she is “concerned” about the matter and that lawmakers “have to take a good look at it.”