Secretary of State Mike Pompeo had said the administration was responding to an emergency caused by Saudi Arabia's arch-foe Iran
President Donald Trump on Wednesday vetoed three congressional resolutions barring billions of dollars in weapons sales to countries including Saudi Arabia and the United Arab Emirates.
The resolutions "would weaken America's global competitiveness and damage the important relationships we share with our allies and partners," Trump said in letters to the Senate justifying blocking them.
It is the third time the president has employed his veto power since taking office.
The measures cleared Congress this month in a strong rebuke to Trump, whose administration took the extraordinary step of bypassing legislators to approve the sales in May.
Secretary of State Mike Pompeo had said the administration was responding to an emergency caused by Saudi Arabia's arch-foe Iran.
But lawmakers including some Senate Republicans said there were no legitimate grounds to circumvent Congress, which has the right to disapprove arms sales.
Senator Lindsey Graham delivered a stinging rebuke to Riyadh last month, saying he hoped his vote against the sales would "send a signal to Saudi Arabia that if you act the way you're acting, there is no space for a strategic relationship."
The senator was referring to last year's brutal murder of journalist Jamal Khashoggi in Turkey at the hands of Saudi agents, an incident that outraged lawmakers and triggered a full-blown crisis in Riyadh's relations with the West.