Media playback is unsupported on your device Media caption The operation is expected to take place on Friday, as the BBC's Nicholas Witchell reports

The Duke of Edinburgh has been admitted to hospital for an exploratory operation, Buckingham Palace has said.

The duke was admitted to the London Clinic "following abdominal investigations" and is expected to stay in the hospital for up to two weeks.

The operation will take place on Friday under general anaesthetic. It is a planned, not an emergency, admittance.

Prince Philip, who will be 92 on 10 June, pulled out of an official engagement earlier this week.

In the past week, the duke has been having unannounced "abdominal investigations" at the hospital in central London, said BBC royal correspondent Peter Hunt.

The Palace said in a statement that "further updates will be issued when appropriate".

On Monday, Prince Philip pulled out of an engagement for the Royal National Institute of Blind People after becoming unwell ahead of last week's service marking 60 years since the Queen's coronation.

Analysis Away from the public gaze, in the last week, Prince Philip has been slipping in and out of the London Clinic for what the Palace has called "abdominal investigations". These were prompted by routine tests which showed that something was amiss. The precise nature of the problem is not in the public domain. Royals, like others, are allergic to the dissemination of too much medical information. But whatever it is that has been discovered will now be tackled by an "exploratory operation". The patient - a reluctant one at the best of times - is said to be in "good spirits". Officials talk of the mood in Buckingham Palace being "calm". But all of this can't mask the fact that the Queen's husband is poised to turn 92; and he is to undergo surgery under general anaesthetic.

Philip attended the service at Westminster Abbey on Tuesday and was present at a garden party attended by the Queen at Buckingham Palace on Thursday afternoon.

Guests said he gave no signs of being unwell.

According to the BBC's royal correspondent, Prince Philip was driven to the clinic after the party and walked in unaided.

A Buckingham Palace spokeswoman said: "He is in very good health."

She added: "He felt unwell on Monday and missed an engagement, but that was down to the fact he had temporarily lost his voice."

A Palace spokesman at the London Clinic described the Duke of Edinburgh as being in good spirits.

The spokesman stressed it was not an emergency admission and the decision was taken by the duke's doctors to carry out the exploratory operation after investigations and tests last week.

Police officers were standing guard outside the hospital ahead of Philip's operation.

In April, Buckingham Palace played down fears about the Duke of Edinburgh's health after he was pictured with purplish skin round his eye in Canada. It said he did not fall and simply woke up with the discoloration.

Prince Philip, 91, has been admitted to hospital three other times in the past two years after suffering health scares.

Media playback is unsupported on your device Media caption The BBC's Ben Ando reports from the London Clinic where the media is gathered

In August 2012, he was treated at Aberdeen Royal Infirmary for a bladder infection.

He spent four days in hospital over Christmas 2011, following an operation to clear a blocked heart artery.

After attending events to mark the Queen's Diamond Jubilee in June, he was admitted to hospital for five nights missing several days of festivities after sustaining a bladder infection.

Writing on Twitter, Prime Minister David Cameron said: "My best wishes to the Duke of Edinburgh who is in hospital tonight. I hope he has a swift recovery."

On Friday, Prince Philip was due to accompany the Queen when she officially opens the BBC's New Broadcasting House building in central London. The Queen will now undertake the visit alone.

Prince Philip's health August 2012 - spends night in hospital after recurrence of bladder infection

June 2012 - taken to King Edward VII Hospital, London, with bladder infection

December 2011 - taken to Papworth Hospital, Cambs, with chest pains - coronary stent fitted

October 2011 - pulled out of trip to Italy due to a cold

June 2010 - had surgery for carpal tunnel syndrome as a day patient at an undisclosed hospital

January 2009 - pulled out of engagements due to back injury while carriage driving on his Norfolk estate

Philip was at the Queen's side at Westminster Abbey on Tuesday for the coronation service and on Wednesday toured a Victorian steamship, the SS Robin, in London's East End.

Ahead of the garden party, the Queen invested her husband with New Zealand's highest honour to mark the Diamond Jubilee making him an additional member of the Order of New Zealand.

BBC royal correspondent Nicholas Witchell said the Duke of Edinburgh would miss the Trooping the Colour parade on 15 June, marking the Queen's official birthday.

Camilla Tominey, royal editor for the Daily Express, told the BBC: "Obviously he was at the garden party this afternoon, so he must have known that he was going into hospital later that day, but decided to carry ahead with that engagement.

"Naturally, Buckingham Palace is reluctant to go into too much detail because it concerns a key member of the royal family's health and personal affairs."