The chairmen of the Senate Ethics Committee put out a statement late Thursday night indicating their investigators had uncovered some improprieties on the part of Sen. John Ensign (R-Nev.).

Ensign announced Thursday he would resign his seat effective May 3, prompting speculation the committee was preparing to close in on the two-term senator.

Committee Chairwoman Barbara Boxer (D-Calif.) and Vice Chairman Johnny Isakson (R-Ga.) put out a short, terse statement saying the committee would "complete its work."

“The Senate Ethics Committee has worked diligently for 22 months on this matter and will complete its work in a timely fashion. Senator Ensign has made the appropriate decision," the statement said.

Despite Ensign's resignation, the committee could still issue a public statement on its investigation.

In February, the Ethics Committee ramped up its investigation of the senator over claims he violated ethics rules in the aftermath of an affair with Cynthia Hampton, the wife of former aide Doug Hampton, whom he then helped to obtain a lucrative lobbying job. The committee named a special counsel to the case.

The Department of Justice and the FBI dropped their respective probes of the senator last year.

Ensign cited the committee's work in his resignation statement Thursday.

"I will not continue to subject my family, my constituents, or the Senate to any further rounds of investigation, depositions, drawn out proceedings, or especially public hearings. For my family and me, this continued personal cost is simply too great," he said.

—Shane D'Aprile contributed.