US President Donald Trump has vetoed congressional efforts to block $8bn in arms sales to Saudi Arabia and the United Arab Emirates that his administration had authorised without the approval of lawmakers.

Wednesday's vetoes come after both the Senate and the House of Representatives passed resolutions to halt the arms deals.

The State Department bypassed Congress to push the sales through by declaring an emergency, citing growing tensions with Iran.

The Senate will vote within the next few days on whether to override Trump's veto, Majority Leader Mitch McConnell said.

McConnell said the vote would be held before 2 August, when lawmakers leave Washington for a five-week-long recess.

However, the three resolutions of disapproval are not expected to garner the two-thirds majority in the 100-member Senate needed to override the veto.

Only a handful of Trump's fellow Republicans, who hold 53 seats in the Senate, backed the resolutions when they passed last month.

'Reliable partner'

Trump said blocking the deals would damage "the credibility of the United States as a reliable partner".

Congress tried to end US support for Saudi Arabia's war in Yemen. Here's how it failed Read More »

"This resolution would weaken America’s global competitiveness and damage the important relationships we share with our allies and partners," the White House said in a statement late on Wednesday.

Congresswoman Debbie Dingell, a Democrat from Michigan, was quick to denounce the veto late on Wednesday, calling on lawmakers to act against it.

"These arms deals with Saudi Arabia do not serve US interests," Dingell wrote on Twitter.

"There is already a terrible humanitarian crisis in Yemen, and we cannot be complicit in worsening the crisis. The Trump Administration can no longer overstep its authority. Congress must override the veto."

US laws give Congress the power to halt major arms sales to foreign countries.

The decision to sidestep the legislature caused an outcry on Capitol Hill, where many lawmakers, including some of the president's allies, denounced the questionable use of an emergency declaration.

Relationship with Riyadh

The sales were forced through during a time of growing scepticism in Congress towards the US alliance with Saudi Arabia after the murder of Washington Post journalist Jamal Khashoggi and the mounting civilian death toll from the Saudi-led war in Yemen.

Coupled with anger at Riyadh, legislators were furious over the administration's failure to follow the normal process for arms sales. Both chambers of Congress held hearings to question administration officials about the emergency declaration.

Earlier this month, Republican Senator Ted Cruz, a staunch Texas conservative who is close to Trump, decried the State Department's decision to bypass Congress, urging the administration to "follow the damn law and respect it".

"I have to say I agree with the concerns that have been expressed in this hearing on both sides of the aisle," Cruz said at a hearing in the Senate.

Congress has been pushing to hold Riyadh accountable for the death of Khashoggi, who was killed by Saudi government agents at the country's consulate in Istanbul last October.

Trump ignored a deadline mandated by the Global Magnitsky Act, a US human rights law, to report to Congress on whether Saudi Crown Prince Mohammed bin Salman was involved in the murder.

Earlier this year, Trump also vetoed a congressional resolution to halt Washington's support for the war in Yemen.