Source: CNN International
"The Queen remains comfortable and at Balmoral (Castle)," the statement added.
A Royal Source told CNN that immediate family members of the monarch, who is 96, have been informed of the concern for her health.
Her son Prince Charles, along with Camilla, the Duchess of Cornwall and the Queen's grandson Prince William, have traveled to Balmoral.
The Queen met with Britain's new Prime Minister Liz Truss on Tuesday. Truss tweeted Thursday that "the whole country will be deeply concerned by the news from Buckingham Palace this lunchtime."
"My thoughts -- and the thoughts of people across our United Kingdom -- are with Her Majesty The Queen and her family at this time," Truss added.
That meeting would typically have taken place at London's Buckingham Palace, but the monarch has significantly reduced her duties and travel in recent months as she suffered with mobility issues.