BANGKOK (Reuters) - Thailand's King Bhumibol Adulyadej met the country's prime minister and two other ministers on Sunday, helping to ease concern over his health after he was admitted to hospital last month.

King Bhumibol, 86, attended an official ceremony at Bangkok's Siriraj Hospital where he is being treated following an operation to remove his gallbladder.

Prime Minister Prayuth Chan-ocha, a former army chief who led a May coup that helped remove the remnants of an elected government, attended the ceremony with the ministers.

Photographs released by the Royal Household Bureau, which tightly controls information about the royal family, show Prayuth, dressed in a white uniform, bowing and the king sitting on a golden chair.

The meeting was originally scheduled for Friday but the palace said doctors had advised the king to cancel the engagement, raising public concerns over the monarch's health.

The king is revered by many Thais and his portrait hangs in every government building and in many shops and homes.

King Bhumibol, a constitutional monarch, made several interventions in the 1970s and 1990s to call for calm during political upheaval. He was silent during the latest crisis, which began in November and culminated in the coup in May.

Thailand has a strict law which makes it a crime to defame, insult or threaten the king, queen, heir to the throne or regent. A national police spokesman said on Sunday that two senior policemen face royal insult charges in the latest in a mounting number of these cases following the May coup.