WASHINGTON — Homeland Security Secretary Alejandro Mayorkas offered to testify in the House GOP’s impeachment inquiry against him, but the committee chairman leading the probe is accusing him of refusing the panel’s request.

The House Homeland Security Committee officially launched impeachment hearings this week after a yearlong investigation into a border crisis they say Mayorkas has failed to mitigate. Homeland Security Committee Chairman Mark Green, R-Tenn., sent Mayorkas a letter on Jan. 5 asking him to appear for a hearing on Jan. 18.

Green is now accusing Mayorkas of refusing the committee’s request after his staff suggested that they work together to find another date.

In a letter to the committee sent Thursday morning that was obtained by NBC News, the Department of Homeland Security assistant secretary for legislative affairs wrote: “In keeping with the Secretary’s commitment to cooperate with Congressional Committees, he will make himself available to testify before the Committee. Consistent with the customary accommodations process, we look forward to working through the details with Committee staff and agreeing upon the date and structure of the hearing.”

“As you can appreciate, the Secretary’s schedule is quite committed with the work of the Department including hosting Mexican Cabinet Members next week to discuss border enforcement,” the letter said.

Moments after the letter was sent, Green responded in a statement, writing: “It is deeply troubling that Secretary Mayorkas has refused the Committee’s multiple requests to appear before a co-equal branch of government. For months, we have tried to work with his office to secure his testimony before the Committee so the American people can receive some much-needed transparency about the causes, costs, and consequences of the unprecedented border crisis.”

The GOP effort to impeach Mayorkas comes as the DHS secretary is actively working with a bipartisan group of senators on a deal to enhance immigration enforcement and send more resources to the southern border.

Green’s initial request to Mayorkas requested a response by Jan. 10, and committee staff familiar with the matter said their first communication with DHS about the request came in a phone call that evening and that they gave DHS an extension on their response on the morning of Jan. 11. The committee staff would not say whether they would engage with DHS to schedule another time for an appearance, citing previous examples in which they asked him to come testify on the border crisis, and DHS opted to have Mayorkas testify at the Annual Worldwide Threats Hearing instead.

“This is just them being unreasonable and also a delay tactic,” a member of committee staff said. “This is the third time he’s turned us down.”

In lieu of an appearance from Mayorkas, the committee will hold a hearing on Jan. 18 titled, “Voices for the Victims: The Heartbreaking Reality of the Mayorkas Border Crisis.”

This article was originally published on NBCNews.com