WASHINGTON — President Trump on Friday amped up the mystery surrounding first lady Melania’s recent hospitalization for a kidney condition, revealing that she had had a “big operation” that lasted close to four hours but is “doing great.”

Trump said he was attending meetings in Canada and Singapore alone because the first lady is under doctors’ orders not to fly for a month.

“The first lady is great. Right there,” Trump said, pointing up to the White House from the driveway as he departed for Quebec. “And she wanted to go. Can’t fly for one month, the doctors say. She had a big operation. That was a close to a four-hour operation. And she’s doing great.”

Trump’s comments only deepened the mystery surrounding his wife’s hospitalization in mid-May and her weekslong absence from the public eye.

The first lady’s office announced May 14 that she underwent an embolization procedure to treat a kidney condition described as benign. She spent five nights at Walter Reed National Military Medical Center outside Washington and returned to the White House on May 19 to continue her recuperation.

Stephanie Grisham, a spokeswoman, has declined to provide additional details, citing the first lady’s right to medical privacy.

Doctors not involved in Mrs. Trump’s care but familiar with the procedure said embolization most likely was used to remove a type of noncancerous kidney tumor called an angiomylipoma. Embolization is a minimally invasive procedure in which doctors snake a catheter into blood vessels of the kidney to find the one that is feeding the tumor and block it off.

Dr. Lambros Stamatakis of MedStar Washington Hospital Center said embolization can take hours because of the time needed to find the right blood vessel. Trump’s four-hour estimate could cover when his wife was wheeled off to receive anesthesia and time in the recovery room, Stamatakis said.

He said that with a VIP, doctors “may take a couple extra hours to make sure everything is as perfect as it possibly can be.”