Conservative groups seeking tax-exempt status were more closely scrutinized by the Internal Revenue Service than their progressive counterparts, according to a report Tuesday by House Republican investigators.

Tea party and other conservative groups were, on average, asked three times as many questions as progressive groups, said the report by Republicans on the House Ways and Means Committee. Conservative groups were less likely to be approved for tax-exempt status and more likely to have their applications delayed, the report said.

The IRS has been under siege since May when agency officials acknowledged that agents working in a Cincinnati office had improperly targeted tea party groups for extra scrutiny when they applied for tax-exempt status. The IRS has since released documents suggesting that progressive groups may have been targeted, too.

Democrats in Congress have highlighted the possibility that liberal groups were also abused to counter charges by some Republicans that that the targeting was politically motivated.

“The facts are very clear — not only were conservative groups targeted by the IRS, but they received much higher scrutiny than progressives,” said Rep. Dave Camp, R-Mich., chairman of the Ways and Means Committee.

“However, this is just the tip of the iceberg,” Camp said. “We have received less than 3 percent of the documents responsive to the investigation. So, Congress will continue to investigate how the targeting began, why it was allowed to continue for so long and what the IRS is doing to resolve this. Americans deserve to know the full truth.”

The IRS said in a statement that 70 agency lawyers are working full-time to review documents for congressional inquiries.

A report by the IRS inspector general said the agency gave extra scrutiny to 298 groups when they applied for tax exempt status from the spring of 2010 to the spring of 2012.

A total of 104 applications included the labels “conservative,” ”tea party,” ”patriot” or “9-12” in their names, according to the Ways and Means report, which is consistent with the inspector general’s report. Seven included the words “progressive” or “progress.”

While processing the applications, IRS agents asked the progressive groups an average of 4.7 questions and eventually approved all seven applications, according to the analysis by Ways and Means Republicans. Some progressive groups, however, complained about lengthy delays.

The conservative groups were asked an average of 14.9 questions and, as of May 31, only 48 applications had been approved. The other 56 applications were either pending or withdrawn. None was denied.

Rep. Sander Levin of Michigan, the top Democrat on the Ways and Means Committee, said the analysis omits other liberal or progressive groups that don’t have the word “progressive” in their names.

“This is a recurring problem in this investigation — the release of incomplete information,” Levin said. “Indeed, that is exactly what led to fundamental flaws in the (inspector general’s) report.”