WASHINGTON — An airport encounter this week between Attorney General Loretta E. Lynch and former President Bill Clinton has welled into a political storm, with Republicans asserting that it compromised the Justice Department’s politically sensitive investigation into Hillary Clinton’s email practices while she was secretary of state.

The Obama administration declined to say on Thursday whether the meeting between Ms. Lynch and Mr. Clinton, in Phoenix on Monday night, was appropriate. The press secretary, Josh Earnest, said that the investigation of Mrs. Clinton would be free of political influence and that he would leave it to the attorney general to explain the meeting.

Ms. Lynch said the meeting with Mr. Clinton was unplanned, largely social and did not touch on the email investigation. She suggested that he walked uninvited from his plane to her government plane, which were both parked on a tarmac at Phoenix Sky Harbor International Airport.

“He did come over and say hello, and speak to my husband and myself, and talk about his grandchildren and his travels and things like that,” Ms. Lynch said at a news conference in Los Angeles on Wednesday, where she was promoting community policing. “That was the extent of that. And no discussions were held into any cases or things like that.”