The UAE has declared three days of mourning following the death of Sheikh Sabah Al Ahmed, Emir of Kuwait.
Sheikh Sabah passed away on Tuesday at the age of 91 and his death was announced by the Emiri Diwan.
"With deep sadness and sorrow the Emiri Diwan sends its condolences to the people of Kuwait, the Arab and Muslim nations, and our friendly nations worldwide," it said.
The UAE's leaders paid tribute to Sheikh Sabah, who they said was a beacon of tolerance, wisdom and peace.
The President, Sheikh Khalifa, said the Arab world had lost a leader of great stature who always strove to mend fences.
He said Sheikh Sabah worked tirelessly for his country and all Arab nations until the last moment of his life and he mourned his death with great sadness.
A Ministry of Presidential Affairs statement expressed condolences to the Al Sabah family and the Kuwaiti people.
"We emphasise our full confidence in the farsightedness, fortitude and the ability of the people of the state of Kuwait and their wise leadership to complete the triumphant journey of the late Sheikh Sabah Al Ahmad in serving the nation and advancing the course of joint Arab action," it said.
The period of mourning began on Tuesday and flags shall fly at half-mast at all official departments inside the country and the embassies and diplomatic missions of the UAE abroad. Classical music typically plays on the radio.
Sheikh Mohammed bin Rashid, Vice President and Ruler of Dubai, said he was a compassionate ruler and the heart of the Arabian Gulf.
"May God have mercy on the compassionate father of Kuwait ... We belong to Allah and to Him we shall return," said Sheikh Mohammed on Twitter.
Sheikh Mohamed bin Zayed, Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces, also paid tribute.
"Our sincere condolences go to the Al Sabah family and the people of Kuwait," said Sheikh Mohamed on Twitter.
"Sheikh Sabah epitomised wisdom, tolerance, and peace and he was a great pioneer of Gulf cooperation.
"He served Kuwait with honour and grace, and his work will never be forgotten. May God have mercy on him."
Sheikh Sabah was admitted to hospital in the United States in July following surgery.
He ruled Kuwait since 2006 and has steered its foreign policy for more than 50 years.
Emir of Kuwait dies, aged 91
Sheikh Saud bin Saqr Al Qasimi, Ruler of Ras Al Khaimah, said Sheikh Sabah was a symbol of peace, wisdom and a constant supporter of the issues affecting Arab and Islamic nations.
"He led Kuwait into the modern age, on a path to stability and prosperity, winning the respect and appreciation of the entire world in the process. I send my sincere condolences and sympathy to Kuwait’s ruling family and to the country’s brotherly people, as they face this great loss," said Sheikh Saud.
"We ask God Almighty that the deceased is granted mercy and that his family find patience and solace."
Sheikh Hamdan bin Mohammed, Crown Prince of Dubai, said the world would miss an exceptional leader.
Peace, human leadership, progress and passion for making a better future for Kuwait and our region. We will miss an exceptional leader, leaving a legacy of generosity and humanity," said Sheikh Hamdan.
"We ask God to embrace him with the breadth of his mercy and inspire our people in Kuwait with patience and solace."
