House Oversight Committee Chairman Darrell Issa on Wednesday abruptly adjourned a hearing over the IRS' targeting of conservative groups after former agency official Lois Lerner refused to answer his questions.

Issa had called the hearing to hear testimony from Lerner, who headed the IRS agency handling tax-exempt organizations. But Lerner declined to answer questions on the advice of her counsel, pleading the Fifth Amendment.

After asking questions for some 20 minutes without getting a response from Lerner, Issa abruptly adjourned the committee hearing, without giving Democrats on the panel a chance to make a statement.

Republicans on the committee say that Lerner waived her Fifth Amendment rights in a prior committee hearing in May 2013 where she denied any wrongdoing, but Democrats — and Lerner’s attorneys — disagree.

Issa's move prompted a furious row between him and the committee's top Democrat, Rep. Elijah Cummings, Md. Having gavelled out the meeting, Issa and Republicans cleared the room and cut off Cummings' microphone.

Issa could be heard in the background, calling for the room to be cleared.

"We're adjourned," he said. "Close it down."

"You cannot run a committee like this. ... I am a member of the Congress of the United States of America," Cummings yelled, as Republicans began clearing the room.

"I am tired of this,” Cummings continued. “It's absolutely un-American."

Cummings went on to call the probe a "one-sided investigation."

Democrats charge that a year's worth of reviewing documents and interviewing witnesses has not yielded evidence to support conservative claims that top IRS officials -- and possibly the White House -- conspired against Tea Party groups seeking tax exemption. They say the IRS operation unfairly targeted both conservative and liberal groups.

But Republicans accuse IRS officials of stonewalling their probe and say questions still remain about whether the targeting was politically motivated to help Democrats in the 2012 election.

This story was published at 10:32 a.m. and has been updated.