WASHINGTON - First lady Melania Trump, who spent five nights in the hospital following a kidney procedure, has been out of public view for 15 days running - an unusually long absence even for a first lady who relishes life outside the spotlight.

The first lady was last seen on May 10 standing alongside her husband at Andrews Air Force Base as the couple greeted three Americans who had been released from prison in North Korea. The next day, the White House announced that she had undergone an successful embolization procedure at Walter Reed National Military Medical Center to treat a benign kidney condition.

Although medical experts have said the kind of procedure Melania Trump had typically requires only a night's hospitalization, White House and East Wing aides have said nothing more about the first lady's condition and instead asked for privacy.

This week her office did not say when she planned to resume public events, but says she has been holding meetings with her staff. "We've had several internal staff meetings in the past week around a variety of topics, including her initiatives," Stephanie Grisham, the first lady's spokeswoman said in an email.

Still there is an air of mystery. Friday morning, a reporter shouted a question to the president about a his wife's whereabouts as he prepared to board Marine One to attend the Naval Academy commencement.

According to a pool report, Trump responded by pointing to a window in the White House residence, and said: "She's doing great. She's looking at us right there."

Reporters turned to look at the spot he indicated, but there was no sign of the first lady.

There are few other clues about her movements. Longtime friend Paolo Zampolli says he's exchanged several text messages with Melania Trump since her return from the hospital.

"She seems to be recovering well," he said, though he offered no further details.

The first lady has tweeted a few times in the past two weeks, including a thank-you to the hospital staff and a recognition of Medal of Honor recipient Britt Slabinski, a Navy SEAL who oversaw a daring rescue mission in Afghanistan. President Trump presented Slabinski with the medal Thursday at a White House ceremony that the first lady did not attend.

Melania Trump's prolonged absence from public life comes just as she was posed to take on a more prominent role.

Earlier this month, the first lady had launched her long-awaited signature initiative, "Be Best," which she described as a wide-ranging effort aimed at helping children.

"I will make every effort to 'be best' at championing the many successful well-being programs in existence today that teach the tools and skills for emotional, social, and physical well-being," she said during a Rose Garden speech in which she outlined plans including meeting with tech executives about children's' online habits.

In her absence, others have stepped in to perform the duties that traditionally fall to the president's spouse. On May 22, Karen Pence, the wife of Vice President Mike Pence, accompanied the South Korean president's wife, Kim Jung-sook, on a tour of a historic home near the White House.

"Wonderful visit with Mrs. Kim Jung-sook, the First Lady of the Republic of Korea," Karen Pence tweeted alongside pictures of the two women. "We toured the beautiful and historic Decatur House ... and enjoyed a lovely lunch."

Melania Trump has also not been present for several other White House events that first ladies usually attend. On Wednesday, White House Social Media Director Dan Scavino posted photos of a meeting in the Oval Office with some of the service members the president had met while visiting his wife in the military hospital where she had undergone surgery.

"He told them that when they got out, to come visit him at the @WhiteHouse anytime," Scavino wrote.

Melania Trump was not shown in the photos.