Oman's culture minister Haitham bin Tariq has been sworn in as royal ruler after the death of his cousin Sultan Qaboos, who transformed his nation and became a vital mediator in a turbulent region.

Qaboos, who died on Friday at the age of 79 as the longest-serving leader of the modern Arab world, came to power in 1970 when he deposed his father in a palace coup.

Oman's Sultan Qaboos bin Said, the Mideast's longest-ruling monarch who seized power in a 1970 palace coup and pulled his Arabian sultanate into modernity while carefully balancing diplomatic ties between adversaries Iran and the U.S., has died. He was 79.

The state-run Oman News Agency announced his death early Saturday on its official Twitter account. The sultan was believed to have been in poor health and traveled to Belgium for what the court described as a medical checkup last month. The royal court declared three days of mourning.

Oman said Friday it was trying to reduce spiraling tensions between the United States and Iran as the Pentagon confirmed it was considering deploying more troops to the region.

Voters in Oman headed to the polls Sunday to choose municipal councilors in only the second local election held in the Gulf sultanate.

Oman on Wednesday said it regretted the "unacceptable" attacks on Saudi missions in Iran but did not announce any measures against the Islamic republic, after some Gulf nations downgraded diplomatic ties.

The Omani reaction comes four days after protesters torched Riyadh's embassy and its consulate in Iran over Saudi Arabia's execution of Sheikh Nimr al-Nimr, a prominent Shiite cleric accused of fomenting sedition in the Sunni-ruled kingdom.

Oman's air force has evacuated three U.S. citizens from war-torn Yemen to the Omani capital Muscat following a request for aid from Washington, the sultanate's foreign ministry said Thursday.

Oman "coordinated with Yemeni authorities to find them (the Americans) and allow them leave" late Wednesday from the airport in Yemen's rebel-controlled capital Sanaa, the ministry said in a statement carried by state news agency ONA.

Air raids by Saudi-led coalition warplanes killed 15 people in Yemen's capital in one of the heaviest nights of bombardment in months, aid workers and witnesses said Saturday.

One rescuer told AFP at least 10 civilians were among the dead.

Saudi-led coalition warplanes heavily bombarded rebel positions across the Yemeni capital Saturday, ahead of expected U.N.-mediated peace talks, witnesses said.

They targeted arms depots and military camps in the rebel-held capital's northern districts.

Muscat and Damascus agreed to work together to end Syria's brutal war, official media reported, as the Syrian foreign minister Thursday made his first Gulf visit since the conflict erupted in 2011.

Foreign Minister Walid Muallem met Oman's chief diplomat Yussef bin Alawi to discuss "several regional and international topics of common interest," the official Omani news agency ONA said.

Iran's nuclear deal with major powers will boost "security, stability and regional cooperation," President Hassan Rouhani told Oman's Sultan Qaboos, state news agency IRNA reported Friday.

"Contrary to the opinion of some in the region, this agreement will actually reinforce security, stability and cooperation between neighbors," Rouhani told the Omani leader in a telephone call.