Saudi Arabia has expressed anxiety over the deal reached Sunday in Geneva with Iran by the world powers.
It's a majority Sunni country while Iran is majority Shiite. And like Israel, Saudi Arabia is troubled by Iran's growing clout in the Middle East.
"We don't know all the details yet, but the Saudi government has been very concerned about these negotiations with Iran and unhappy at the prospect of a deal with Iran," a Saudi government official said earlier this week. "There is a lot of worry right now about threats to the region."
On Sunday, Abdullah al-Askar, chairman of the foreign affairs committee in Saudi Arabia's Shoura Council, said people in the Middle East will lose sleep over the nuclear.
Riyadh has frequently called for Washington to maintain a tough line with Tehran.
"I am afraid Iran will give up something on to get something else from the big powers in terms of regional politics. And I'm worrying about giving Iran more space or a freer hand in the region," he told Reuters.
"The government of Iran, month after month, has proven that it has an ugly agenda in the region, and in this regard no one in the region will sleep and assume things are going smoothly," Askar said.
In the hours before Sunday's deal was sealed, Gulf Arab leaders, including Saudi King Abdullah and the rulers of Qatar and Kuwait, met late on Saturday night to discuss "issues of interest to the three nations".
The Gulf Arab rulers, all Sunni Muslims, are enemies of Shi'ite Iran, which backs Syria's President Bashar al-Assad in a civil war in which they back the rebels. They have accused Tehran of fomenting unrest in a range of countries including Yemen, Bahrain, Lebanon and Iraq.
"The people of the region know Iranian policies and Iranian ambitions. And they know that Iran will interfere in the politics of many countries in the region," Askar added.
In recent months Saudi Arabia has grown increasingly anxious about Washington's apparent willingness to deal with Iran's new President Hassan Rouhani and complained about President Barack Obama's reluctance to take tougher action in Syria's civil war.
According to Askar, if the deal did not succeed in preventing Iran from building a bomb, Saudi Arabia and other countries would probably seek one too.
"I think Saudi Arabia will go ahead if Iran goes ahead. I think Egypt, maybe Turkey, Saudi Arabia, maybe the Emirates, would go ahead and acquire the same technology. This will open the door widely to weaponisation."