The Duke and Duchess of Cambridge reacted with "anger and disbelief" after the publication of topless photos of Kate in a French magazine, believing "a red line has been crossed".
The couple "have been hugely saddened to learn that a French publication and a photographer have invaded their privacy in such a grotesque and totally unjustifiable manner", Clarence House said.
The magazine, Closer, has exclusive pictures of Kate topless on the terrace of a private chateau owned by the Queen's nephew Lord Linley.
Its website shows an image of the front cover with the Duchess in a bikini about to remove her top.
Closer magazine in France belongs to Mondadori, owned by Italy's former president Silvio Berlusconi's holding company Fininvest - not the same company as the British title.
Closer magazine UK, published by Bauer Consumer Media, said in a statement: "Closer magazine UK would like to make it clear that the two publications make entirely independent editorial decisions.
"Closer magazine UK was not offered any pictures of this nature and certainly has no intention of publishing the photographs of the Duchess of Cambridge which have been published in France this morning."
St James's Palace has confirmed that the topless pictures are of Kate but have yet to comment further about the images, which are likely to over shadow the royal couple's visit.
A source said the reaction by the Duke and Duchess to the images appearing was "anger and disbelief", although the couple, who have had a busy day of events in Kuala Lumpur, had not seen the actual topless photographs.
It added "They can't believe the pictures were taken, they can't believe anyone would publish them. The level of intrusiveness means a red line has been crossed."
The couple may seek redress through the French legal system as the source added: "We are consulting with French lawyers at the moment."
The source said once they had a break in their schedule the couple would "turn their minds to what, if any, action they wish to take".
The BBC's royal reporter Nicholas Witchell said it appeared British newspapers were offered the alleged photographs of the couple last week, but turned them down.
Alluding to the death of Princess Diana, William's mother, killed in a Paris car crash in 1997 as she was chased by paparazzi, a source told the Daily Mail: 'This incident turns the clock back 15 years.'
The pictures were taken while Kate was on holiday with her husband in France last week.
The couple were staying at the Provence chateau, ahead of their current Diamond Jubilee tour of south-east Asia and the South Pacific on behalf of the Queen.
The publication would restart the row over privacy which raged around Prince Harry last month, when embarrassing images emerged of him frolicking naked in a Las Vegas hotel.
The Sun was the only British newspaper to defy a Press Complaints Commission advisory note not to publish photos of Harry in the nude with an unnamed woman.
The Mail said that the pictures of the Duchess were clearly taken on private property using cameras with extremely long lenses, which means no British newspaper would publish them.
The timing of publication could not be worse, with the Cambridges almost midway through a hugely successful tour on behalf of the Queen to celebrate her Diamond Jubilee.
They arrived in Singapore on Tuesday and are currently in Malaysia before travelling on to Borneo then the South Pacific.
Malaysia is a largely Muslim country with laws on public decency which makes the timing of the photos even more difficult.
At the Assyakirin Mosque in Kuala Lumpur on Friday the couple arrived to find two seats waiting for them at the bottom of marble steps, leading up to the domed place of worship, so they could take off their shoes.
Kate wore a grey dress by Eulah London with a matching headscarf and in keeping with Islamic custom when visiting a mosque, her outfit had sleeves and the hem of the gown was below the knee.
The Duchess's nude LK Bennett heels slipped off easily to reveal stockinged feet, while the Duke had on black socks.
At the top of the steps they were greeted by the Imam of the mosque Ustaz Saiful, director of Islamic religious department Datuk Che Mat Bin Che Ali, chairman of the mosque Syed Abdullah, general manager of facilities Shausudin Ishak and head division development manager Datin Faudziah Ibrahim.
In front of them were row after row of pillars and the party strode through the one-and-a-half acre site built in 1997 which can cater for up to 12,000 worshippers at the height of Friday prayers, with space for a further 3,000 in the grounds.
As they were guided into the large space, William asked "So is this where everyone gathers? When is your biggest service? How many people gather here?" When he was told as up to 12,000 on Fridays, he exclaimed: "Wow. So many."
The Duchess, whose scarf matched her outfit and framed her face, was deep in discussion with the development manager with the royal telling her "It's so peaceful in here", adding: "It's really amazing."
When she mentioned she had been to Edinburgh University for her degree and masters, Kate said: "Oh wow, really? Well it's very cold there compared to here," and the two both covered their mouths giggling.
In front of them were five men sitting crossed-legged on the floor chanting passages from the Koran, which was help open on small tables in front of them.
The royals looked up at a dome above them which was decorated with writings from the Koran and through the windows of the roof could be seen the looming Petronas towers, Kuala Lumpur's famous landmark.
Before leaving the royals stopped to watch three men performing their ablutions - washing face, ears, hands and feet - that must be performed before prayers can be made.
The trio were bent over running taps oblivious to the royals watching them complete the ritual.
The royal couple sat down at their starting point to replace their footwear and William handed Kate her shoes before tying his laces, and the Duchess joked with her partner telling him "mine are easy".
The morning has been full of drama for the Royal couple, after a man intent on giving the Duchess of Cambridge a flower sparked a security scare today when he got close to the royal in Malaysia.
The individual, described by officials as an enthusiastic royal fan, approached Kate with the bloom as she got into a limousine but he was quickly detained by Malaysian police and taken away.
The incident happened after the royal couple - on a Diamond Jubilee tour of the Far East - had taken part in a walkabout during a cultural show of music and dance staged in a park in the heart of Kuala Lumpur.
It is thought he tried to throw the flower into William and Kate's chauffeur driven limousine just before they left the site, and one eyewitness claims the man was able to get his upper body into the vehicle.
The man was reportedly spotted in Singapore at a royal event where the Duke and Duchess began their tour and at different points in the crowds today.
A St James's Place spokesman stressed that at no point were the Duke and Duchess in danger.
He said: "An enthusiastic member of the crowd approached their Royal Highnesses' car today as it departed the cultural event, he appeared to want to throw a flower in the car, a Malaysian protection officer pulled him away."
Later on Friday, William and Kate will also enjoy a Diamond Jubilee tea party hosted by Simon Featherstone, the British High Commissioner to Malaysia, and his wife Gail at their residence.
At the end of the day, the royal couple will leave mainland Malaysia and fly to Kota Kinabalu, capital of the state of Sabah on Borneo, from which they will travel into the rainforest jungle tomorrow to explore the habitat.