The Prime Minister has expressed his sadness at the death of Saudi Arabia's King Abdullah, and paid tribute to his work for peace in the region.

The king died yesterday aged 90, and his successor is to be his 79-year-old half-brother, Prince Salman.

David Cameron, who visited Saudi Arabia in 2012, said: "I am deeply saddened to hear of the death of the Custodian of the Two Holy Mosques, His Majesty King Abdullah bin Abd Al Aziz Al Saud.

"He will be remembered for his long years of service to the Kingdom, for his commitment to peace and for strengthening understanding between faiths.

"My thoughts and prayers are with the Saudi Royal Family and the people of the Kingdom at this sad time.

"I sincerely hope that the long and deep ties between our two Kingdoms will continue and that we can continue to work together to strengthen peace and prosperity in the world."

Mr Cameron's meeting with the King three years ago was a visit intended "to broaden and deepen the UK-Saudi partnership on issues from social development to security to business relations".

The Prime Minister spoke with the King in a telephone call last year on issues including the threat from Islamic State. He thanked the King for a "significant" donation to the humanitarian appeal in Iraq.

King Abdullah was also considered a strong US ally and, following his death, President Barack Obama praised him for taking "bold steps" to help with the Arab Peace Initiative.

Mr Obama said he " valued King Abdullah's perspective and appreciated our genuine and warm friendship".

The King was born in the Saudi Arabian capital of Riyadh in 1924, and became crown prince in 1982, before ascending to the throne in 2005.

Foreign Secretary, Philip Hammond said he was sad to hear the news of the King's death.

He said: " He served the Kingdom of Saudi Arabia for many years with great dignity and dedication. His contribution to the prosperity and security of the Kingdom and the region will long be remembered.

"I would like to offer my sincere condolences to the Kingdom of Saudi Arabia and its people at this sad time."

Former prime minister Tony Blair said he was "very sad" to hear of King Abdullah's death.

He said: " I knew him well and admired him greatly. Despite the turmoil of events in the region around him, he remained a stable and sound ally, was a patient and skilful moderniser of his country leading it step by step into the future.

"He was a staunch advocate of inter faith relations. He founded Kaust, the science and technology university where women and men are educated equally. And today there are more women in higher education than men.

"He allowed thousands to be educated abroad people who have experience of the world and will play a big part in the future of the country. He appointed women ministers. He invested in renewable energy. And of course he launched the Arab Peace Initiative in 2002 which has stood the test of time as a potential basis for a solution to the Israeli Palestine issue.

"He was loved by his people and will be deeply missed."

Saudi Arabia is a nation relentlessly under pressure to reform while also fighting extremist violence.

The country is a monarchy and it is seen as the duty of the citizens to obey their king. There is no elected parliament.

Beheadings and floggings are among the harsh punishments that are inflicted for various crimes under its interpretation of Islamic law.

Fears are growing over the health of blogger Raif Badawi, 31, who was sentenced last May to 10 years in prison and 1,000 lashes for "insulting Islam" and disobedience.

This week's flogging of 50 lashes was postponed for the second week in a row after when doctors argued against it on health grounds but there is still concern about whether a determined Saudi Arabia will resume the punishment.

Amnesty International , which is campaigning for his release, said a doctor had found that his wounds from the first set of lashes delivered in the city of Jeddah on January 9 had not yet healed. It drew immediate worldwide protest. Mr Badawi is sentenced to be lashed 50 times each in 20 weekly sessions.

Sweden's foreign ministry summoned Saudi Arabia's charge d'affaires while the US State Department and the UN High Commissioner for Human Rights called for the punishment to be stopped.

Al Qaida has grown alongside the leaderships blanket refusal to accept any kind of opposition. Saudi nationals were among those who carried out the September 11 2001 terror attacks on New York and Washington.

Saudi Arabia's large Shia minority has become more vigorous about calling for civil rights.

King Abdullah's death brings to an end the reign of a monarch who had to work both with desert traditions and the demands of the modern world.

Although a reformer, he did not change the House of Saud's grip on power. Critics found themselves in prison or silenced.