A Saudi court Tuesday sentenced 15 people to death for spying for the kingdom's rival Iran, local media and a source close to the case said, in a move likely to heighten regional tensions.

The source told AFP that most of the 15 Saudis were members of the kingdom's Shiite minority.

Saudi Arabia's energy minister said Wednesday that an "optimistic" sentiment prevailed at an OPEC meeting meant to agree the cartel's first oil output cut in eight years.

"We don't know (if a deal will be reached)," Khaled al-Falih told reporters in Vienna as the talks started. "We will find out during the meeting. I think the sentiment generally is optimistic and positive."

Arid Saudi Arabia could need more than $53 billion in water sector investment supported by private funds as demand grows, officials said on Sunday.

Iran has sentenced protesters accused of attacking Saudi Arabia's embassy in response to the execution of a prominent cleric to up to six months in prison, their lawyer said Friday.

Saudi Arabia's financial position remains strong despite sinking oil prices, although there is "some pressure" on bank liquidity, the finance minister has said.

A seven-fold hike in visa fees to do business in Saudi Arabia risks deterring the foreign investment needed to transform its oil-dependent economy, diplomats and other sources say.

Saudi Arabia is conducting live-fire drills during war games underway in the Gulf, official media said on Tuesday, as tensions simmer with Iran.

The Saudi-led coalition fighting in support of Yemen's government has killed a senior Yemeni rebel leader on the border, a source close to the coalition said on Saturday.

President Barack Obama is poised to veto legislation exposing Saudi Arabia to court action over the 9/11 attacks, stepping in to defend legal precedent and an awkward ally, but inviting election-time opprobrium.

White House officials say Obama will reject the "Justice Against Sponsors of Terrorism Act" by a Friday veto deadline, after a little over a week of deliberation.

Unidentified gunmen killed two Saudi policemen in the mainly Shiite eastern city of Dammam late on Saturday, the interior ministry said, describing it as a "terrorist attack."