LONDON (AP) — Queen Elizabeth II attended a London reception to celebrate Commonwealth Day on Monday, her first public appearance since she was briefly hospitalized for a stomach illness.

The monarch appeared in good spirits, although earlier in the day she had to pull out of a service at Westminster Abbey. Buckingham Palace officials said the 86-year-old queen was still getting over a bout of gastroenteritis that led to her first hospitalization in a decade last week.

Wearing a mint and silver ensemble, Elizabeth made a brief speech at the ceremony held at Marlborough House in central London. After that she signed a new charter setting out the Commonwealth's values and commitment to equal rights.

The document, agreed upon by the group's 54 member states, commits them to upholding principles, including democracy, rule of law and gender equality.

Earlier Monday, Prince Philip, the queen's 91-year-old husband, attended the service at the abbey, where he was joined by 2,000 guests, including Commonwealth ambassadors.

A prerecorded annual address by the queen, who heads the association of countries, was played in the abbey.

The queen had to cancel several engagements, including a visit to Rome, last week because of her stomach bug. The one-day hospitalization raised concerns about the general health of the queen, who has rarely taken time off her duties due to illness.

But the palace says she remains in robust health.

"The queen hopes to undertake some of her official engagements planned for the rest of the week," the palace said.

Elizabeth carried out more than 400 official engagements in 2012 — ranging from weekly meetings with the prime minister to ceremonial gatherings such as the reception on Monday.