The Attorney General will challenge a Court of Appeal ruling over letters the Prince of Wales wrote to Government ministers.
Hong Kong is acting as the gateway for illegal ivory entering China - where the item is high in demand.
Prince Charles and Prince William joined launched a campaign to save endangered species like rhinos, tigers and elephants from poachers.
A Guardian journalist accused the Attorney General Dominic Grieve of failing to show "reasonable grounds" for blocking the release of letters sent by Prince Charles to government ministers.
The High Court today ruled that Grieve's use of a ministerial veto to stop the letters being published was unlawful but the Attorney General said he will "pursue an appeal."
– A Guardian News & Media spokesperson
The public has a right to know if the heir to the throne is advocating policy or promoting causes to government ministers.
We welcome today's appeal court judgment finding that it was wrong to block the release of the letters.
We hope the Attorney General will recognise he has reached the end of the legal road and that government departments will now publish the correspondence so that the public can judge for themselves.
We are disappointed by the decision in the Evans (Prince of Wales letters) case. To protect the principles at stake we will pursue an appeal
The Attorney General's refusal to let the public see letters the Prince of Wales wrote to government ministers has been ruled unlawful.
Prince Charles has been visiting Saudi Arabia as part of a short tour of the Middle East.
The Prince of Wales joined members of the Saudi royal family to take part in a sword dance, known as an Ardah, in the capital Riyadh.
Charles was wearing the traditional robes for the ceremony, which was celebrating the 17-day-long Janadriyah Festival.
Other highlights of his tour included a visit to the Janadriya gardens and an old Saudi Arabian city.
The Prince is also visiting Qatar in what will be his second visit to the two nations in just under a year, and his 10th official trip to the Saudi Arabia since he first toured the nation in 1986.
Prince Charles will be welcomed in Riyadh by Prince Miteb bin Abdullah bin Abdulaziz al-Saud, chairman of the National Guard when he arrives in the country later today.
– Sir John Jenkins, the UK's ambassador to Saudi Arabia
His Royal Highness' second visit to the kingdom in my time here as ambassador exemplifies our wish to engage at the most senior levels and our determination to sustain the personal touch.
At a time of enormous turmoil and human agony in the Middle East, seen today perhaps most acutely in Syria, the Prince's advocacy of interfaith understanding and dialogue between communities is needed more than ever. His Majesty the King shares this deep concern.
I know that he and His Royal Highness will have much to discuss about the need for reconciliation and their hopes for the region's future.
The Prince of Wales will fly to the Middle East for a short tour. Charles's four-day trip to Saudi Arabia and Qatar comes just under a year since he last toured the two nations.
The heir to the throne's tour has a large majority of private engagements. But highlights of his public events include a tour of an old Saudi Arabian city and in the Qatari capital Doha he will visit a leading museum.
The Duke of Cambridge has hailed tomorrow's major international summit on the trafficking of endangered wild animals as the "beginning of the end of this despicable trade".
Speaking at a Natural History Museum reception attended by conservation charities, philanthropists and leading wildlife campaigners Prince William said:
"Tonight we are here with a single, shared purpose - to use our collective influence to put a stop to the illegal killing and trafficking of some of our world's most iconic and endangered species."
During the event William met one of the world's biggest action movie actors Jackie Chan who is in London to launch an anti-poaching video for the organisation WildAid of which he is an ambassador.
Prince William's decision to go hunting in Spain shortly before he makes a speech at a conservation conference is just 'poor PR' and should not distract from the major issues, an expert has told Daybreak.
Will Travers from the Born Free Foundation said hunting and poaching "were not the same thing", with the latter being a "£12bn international illegal wildlife trade".
Prince William will give a speech tonight to mark the imminent start of an international conference that aims to tackle the threat to the world's endangered animals.
William will make an address at a Natural History Museum reception as world figures prepare to discuss ways of saving animals like elephants, rhinos and tigers tomorrow.
His father Prince Charles will give a speech at the London Conference on the Illegal Wildlife Trade being hosted by the Government at Lancaster House on Thursday. William will also attend and it will be hosted by the Prime Minister.
William has joined forces with the Prince of Wales to record a video message calling on the world to act now to save endangered animals.