Oman’s Sultan Qaboos bin Said, the Middle-East’s longest-serving monarch, has died at the age of 79 after long illness. His death was announced by the state Oman News Agency via its official Twitter account. The royal court in the country declared three days of mourning.

Sultan Qaboos seized power in a 1970 palace coup and reformed his Arabian sultanate into modernity while carefully balancing diplomatic ties between Tehran and the Washington. The new agency phrased his “balanced policy” of mediating between rival camps in a volatile region, which had earned the world’s respect.

The British-educated sultan reformed a nation that was home to only three schools and archaic laws, banning electricity, radios, eyeglasses and even umbrellas when he took the throne.

Under his reign, Oman became known as a popular tourist destination and a key Mideast interlocutor, helping the U.S. free captives in Iran and Yemen and hosting visits by Israeli officials for talks about Palestinian issue.

The European leaders expressed their condolences to the nation.

Oman’s new ruler Sultan Haitham bin Tariq al-Said promised to maintain the Gulf Arab state’s foreign policy of peaceful coexistence and maintaining friendly ties with all nations.