WASHINGTON — The Department of Veterans Affairs’ inspector general is working with federal prosecutors who are trying to determine whether criminal violations occurred at a medical center in Phoenix accused of falsifying data or creating secret waiting lists intended to hide monthslong delays for veterans to see doctors, a top official told a Senate committee on Thursday.

The disclosure by the official, Richard J. Griffin, the acting inspector general for the department, which is carrying out its own inquiry, is the first official indication that prosecutors have taken an interest in the controversy, which has spread in recent weeks to include facilities in Texas, Colorado and other states.

The issue has angered veterans’ groups and prompted several Republican senators to call for the resignation of the secretary of veterans affairs, Eric Shinseki.

At a hearing of the Senate Veterans Affairs Committee, Mr. Griffin said he could not offer many details about the agency’s investigation because “part of this review could lead to criminal charges” and he did not want to impede that process.