Iran Press/America: Donald Trump invoked a rarely used aspect of federal law to push through the $8 billion deal, which would ordinarily need to be approved by Congress.
He did so by declaring that ongoing tensions with Iran amounted to a national emergency.
The move has angered those who fear the weapons may be used against civilians in Saudi Arabia.
Some Democrats have also accused the president of bypassing Congress because of the sale of weapons, including precision-guided munitions and other forms of bombs, would have been strongly opposed on Capitol Hill.
Weapons will also reportedly be sold to the United Arab Emirates and Jordan.
On Friday, Secretary of State Mike Pompeo notified Congress of the administration's decision to make the sale. In a letter, widely reported in US media, he said that "Iranian malign activity" required the "immediate sale" of weapons to Saudi Arabia, UAE and Jordan.
But the move quickly garnered opposition. Democratic Senator Robert Menendez, who sits on the Foreign Relations Committee, accused Donald Trump of "granting favors to authoritarian countries".
"[He] has failed once again to prioritize our long term national security interests or stand up for human rights," he said in a statement.
Republican Foreign Relations Committee chairman, Senator Jim Risch, said he had been informed by the Trump administration that it planned to confirm "a number of arms sales".
"I am reviewing and analyzing the legal justification for this action," he said.
Washington upped the ante against Tehran earlier this month when it ended exemptions from sanctions for countries buying Iranian oil. The decision was intended to bring Iran's oil exports to zero, something which many analysts have said is impossible to do.
Trump reinstated the sanctions against Tehran last year after abandoning the landmark nuclear deal that Iran has signed with six nations - the five permanent members of the UN Security Council and Germany.
America's unilateral abrogation of the multilateral agreement has been criticized by many countries including its traditional European allies such as Britain, France, and Germany.
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