The US Senate has voted to block the sale of billions of dollars' worth of weapons to Saudi Arabia, striking a blow to President Donald Trump.

Mr Trump bypassed Congress last month in an attempt to push through the $8bn (£6bn) deal, citing threats to Saudi Arabia from its bitter rival Iran.

But on Thursday - in a rare bipartisan act - the Republican-led Senate passed three resolutions to prevent the sale.

The president has promised to veto the action, leaving the deal in limbo.

While the Democrat-controlled House of Representatives is also likely to vote to block the sale, analysts say it is almost certain Congress will not have the necessary votes to override a veto from Mr Trump.

The first and second resolutions of disapproval passed by a margin of 53-45 and a third vote, which covered a number of other resolutions relating to the arms sale, passed by 51-45 votes.

As well as Saudi Arabia, weapons would also reportedly be sold to the United Arab Emirates and Jordan under the deal.

Mr Trump bypassed Congress last month by invoking a rarely used aspect of federal law. He declared that ongoing tensions with Iran amounted to a national emergency, meaning the sale of weapons - including precision-guided bombs - was a matter of urgency.

But the move sparked fierce opposition on Capitol Hill from those who feared the weapons may be used against civilians in Yemen by Saudi-led forces.

Just hours before the vote, Iran shot down a US military drone over the Strait of Hormuz.

This escalated fears of a wider conflict and will no doubt reinforce the administration's argument that its allies need these weapons.

President Trump has promised to veto the Senate action in order to proceed with the deals, and lawmakers almost certainly do not have enough votes to override that.

But they will keep up their legislative resistance in other ways, because they are afraid that the administration will try to bypass them over any decision to launch a military strike on Iran.