It comes after Donald Trump used his presidential veto to override resolutions passed by both chambers of Congress preventing the sale.

Critics fear the weapons may be used on civilians in the Yemen conflict.

But Mr Trump had argued that blocking the sale of weapons would "weaken America's global competitiveness".

The president also argued last week that it could damage relations with US allies as he rejected the bipartisan resolutions.

However, a number of lawmakers - including some Senate Republicans - said there was no legitimate reason to bypass Congress.

In Monday's first vote, five Republicans voted to override the president, siding with their Democrat colleagues 45-40. Fifteen senators abstained.

Two further votes had similar margins.

The Trump administration announced in May that it was proceeding with the sale of the weapons to Saudi Arabia and the United Arab Emirates.

Mr Trump issued a national emergency declaration in order to push through the sale.

He suggested that barring it could prolong the conflict in Yemen and that "without precision-guided munitions, more - not fewer - civilians are likely to become casualties".

The president also insisted that Saudi Arabia and the United Arab Emirates were a "bulwark against the malign activities of Iran and its proxies in the region". Tensions between the US and Iran have soared since the US pulled out of a landmark nuclear deal last year and reimposed sanctions.

Public information on Saudi Arabia's military spending is limited, but it is estimated to be the world's largest importer of weapons and the biggest military spender in the Middle East.

It is also the largest customer of US arms exports. According to the Stockholm International Peace Research Institute, around 22% of all US weapons exports went to Saudi Arabia between 2014-18 - up from just 4.9% between 2009-13.

Saudi spending has been boosted by its intervention in Yemen's bloody civil war where it's been supporting exiled President Abdrabbuh Mansour Hadi with air strikes, ground support and aerial and naval blockades against Houthi rebels it sees as an Iranian proxy.

In 2017, President Trump signed an arms deal worth $350bn over a ten year period, hailed as the largest in American history.

But along with humanitarian arguments, critics of Trump argue the economic benefits of such deals are massively inflated.

According to US government figures, the value of American military exports to the kingdom peaked in 2017 but only accounted for 0.27% of all US exports that year.