Queen Elizabeth updates: State funeral ends 11 days of ceremonies

U.S. President Joe Biden has been briefed on Britain's Queen Elizabeth II and "will be updated throughout the day concerning news out of the United Kingdom," given the reports of her health, White House spokesperson John Kirby said Thursday

"His and the first lady's thoughts are solidly and squarely with the queen today and her family," Kirby told reporters.

Biden also expressed that his thoughts are with U.K. Prime Minister Liz Truss, who took office on Tuesday and is currently taking part in a previously scheduled phone call with Biden and other allies focused on "continued support for Ukraine," according to Kirby.

"I can tell you that in this video conference that the president is having as we speak, I can tell you that he did convey to Prime Minister Truss, who is on the video teleconference, that he and Dr. Biden are thinking very much of the queen and the family and the people of the United Kingdom," Kirby said.

-ABC News' Molly Nagle

U.K. Prime Minister Liz Truss took to Twitter on Thursday to say that her "thoughts -- and the thoughts of people across our United Kingdom -- are with Her Majesty The Queen and her family at this time."

"The whole country will be deeply concerned by the news from Buckingham Palace this lunchtime," Truss tweeted.

Truss, who was recently selected as the new leader of the United Kingdom's ruling Conservative Party, had an audience with the queen at Balmoral Castle in Scotland on Tuesday, during which she was formally asked to form a new government as prime minister after Boris Johnson's official resignation. It was the first time in the queen's 70-year reign that the ceremonial transfer of power was held at Balmoral, rather than at Buckingham Palace in London.

Senior members of the British royal family are gathering at Balmoral Castle in Scotland, where Queen Elizabeth II remains "under medical supervision."

The queen's oldest child and the heir to her throne, Charles, Prince of Wales; and his wife, Camilla, Duchess of Cornwall; as well as the queen's daughter, Anne, Princess Royal, are already at Balmoral, according to their respective spokespersons.

Meanwhile, the queen's other sons, Prince Andrew, Duke of York; and Prince Edward, Earl of Wessex; along with Edward's wife, Sophie, Countess of Wessex; as well as Charles' two sons, Prince William, Duke of Cambridge; and Prince Harry, Duke of Sussex, are all on their way to Balmoral, their respective spokespersons confirmed.

Harry's wife, Meghan, Duchess of Sussex, was initially said to be heading to Balmoral as well, but her spokesperson later confirmed she would stay in London for now.