Leaders of a House panel on Tuesday called for more transparency from the Secret Service and criticized the agency's director for being the sole official to testify about an incident earlier this month in which two agents allegedly drove into a White House barricade and disrupted an investigation.

"I'm simply disappointed we will not hear from the other Secret Service witnesses invited here," said Rep. Elijah Cummings (D., Md.), a ranking member of the House Oversight Committee. "No other committee is doing more on this issue than ours."

Cummings and committee Chairman Rep. Jason Chaffetz (R., Utah) called on Secret Service Director Joseph Clancy and several other agency officials on the scene of the March 4 incident to testify.

But in a letter to the committee late last week, Clancy, who over the last two weeks has testified before other congressional committees about the incident, said he would be the lone agency official to sit before the committee. While speaking to lawmakers earlier this month, Clancy said he was "very frustrated" that he did not hear about the incident until five days after it occurred and promised to hold his staff accountable pending an internal investigation.

"I don't think your appearance alone is sufficient for this hearing today," Chaffetz told Clancy in his remarks. He added, "The Secret Service has refused our request" to hear from additional witnesses to get a clearer picture of what occurred.

Lawmakers on Tuesday were investigating allegations that two senior Secret Service agents, purportedly under the influence of alcohol, disrupted an investigation on the White House grounds on the night of March 4. One of the agents is a senior official who works in President Obama's security detail.

Clancy, who was appointed to head the embattled agency in February by Obama, took responsibility for the incident and emphasized to the committee that the agency was investigating it. But he also disputed some reports that agents "crashed" into a barrier, and instead called it a "nudge" by the agents.

In remarks, lawmakers also questioned why some video surveillance of the incident was erased. Lawmakers viewed short video clips of the incident and called for a complete accounting of all footage associated with the incident.

Clancy on Tuesday said all video will be made available to the committee in the near future as the investigation is continuing.