Melania Trump declares her health and marriage are in good shape after not appearing in public for 20 days

First lady takes to Twitter to say she is 'feeling great'

Melania Trump hosts a roundtable discussion with tech leaders on the effects of the Internet on children (Reuters)

After three weeks out of the public eye, Melania Trump has put to rest speculation about her health and marriage.

The first lady, who is recovering from medical treatment for a kidney condition, took to Twitter to say she was “feeling great” and is at the White House.

Ms Trump is yet to make a public appearance, leaving some sceptics still wondering about her condition.

The first lady's tweet landed while her husband was participating in a White House event that seemed tailor-made for a first lady, as famous athletes joined Donald Trump and his daughter and senior adviser, Ivanka Trump, on the South Lawn to promote youth sports and fitness.

"I see the media is working overtime speculating where I am & what I'm doing," Ms Trump said on Twitter. "Rest assured, I'm here at the @WhiteHouse w my family, feeling great, & working hard on behalf of children & the American people!"

Ms Trump has not appeared in public since 10 May, when she accompanied the president to a military base in Maryland to welcome home three Americans who had been released from detention in North Korea.

Four days later, the White House announced that the 48-year-old had successfully undergone an "embolisation" procedure to treat a benign kidney condition, and that there were no complications.

She spent five nights at Walter Reed National Military Medical Centre in nearby Bethesda, Maryland.

Some doctors familiar with the procedure but not involved in her care said people treated with embolisation typically are sent home the same day or the next.

First ladies are under no obligation to make their medical histories public, and the White House has said nothing more about Ms Trump's condition.

On Friday, the president tried to assure reporters that his wife was doing fine.

Asked about the first lady's health before he boarded the presidential helicopter on the South Lawn, Mr Trump pointed to the second floor of the White House and said: "She's doing great. Right there. She's doing great. She's looking at us, right there."

Despite Mr Trump's assurances, reporters didn't see any sign of the first lady watching from above.

Ms Trump is often viewed as a reluctant first lady, but her lengthy absence from public view comes after what was probably her most high-profile period in the role to date.

In April, she alone represented the administration at the Houston funeral of former first lady Barbara Bush. She joined the president to host the Japanese prime minister for talks at the Trumps' estate in Florida. That was followed by the French president's three-day state visit to the White House, which included the first state dinner planned under her watch for more than 100 guests.

Ms Trump capped it off in early May with a splashy Rose Garden rollout for her "Be Best" campaign to teach kindness to children. Mr Trump watched from the audience.

Her popularity is rising, according to a recent CNN poll that found 57 per cent of those surveyed saying they have a favourable impression of her, up from 47 per cent in January.

Agencies contributed to this report