US President Donald Trump, declaring a national emergency because of tensions with Iran, swept aside objections from Congress on Friday to complete the sale of over $8bn worth of weapons to Saudi Arabia, the United Arab Emirates (UAE) and Jordan.

The Trump administration informed congressional committees that it will go ahead with 22 military sales to the three countries, infuriating politicians by circumventing a long-standing precedent for congressional review of major weapons sales.

Members of Congress had been blocking sales of offensive military equipment to Saudi Arabia and the UAE for months, angry about the huge civilian toll from their air campaign in Yemen, as well as human rights abuses.

US Secretary of State Mike Pompeo said on Friday that the weapons sales are needed because any delay could increase risk for US partners at a time of instability caused by Iran.

"These sales will support our allies, enhance Middle East stability, and help these nations to deter and defend themselves from the Islamic Republic of Iran," Pompeo said in a statement, adding that the decision to circumvent Congress was meant to be a "one-time event".

Some politicians and congressional aides had warned earlier this week that Trump, frustrated with Congress holding up weapons sales like a major deal to sell Raytheon Co precision-guided munitions to Saudi Arabia, was considering using a loophole in arms control law to go ahead with the sale by declaring a national emergency.

US arms control law allows Congress to reject weapons sales to foreign countries, however, an exemption in the law allows the president to waive the need for congressional approval by declaring a national security emergency.

"I am disappointed, but not surprised, that the Trump Administration has failed once again to prioritise our long-term national security interests or stand up for human rights, and instead is granting favours to authoritarian countries like Saudi Arabia," Senator Bob Menendez said in a statement.

Menendez is one of the members of Congress who reviews such sales because he is the ranking Democrat on the Senate Foreign Relations Committee.

He said that the administration, in explaining its intervention, "described years of malign Iranian behaviour". But Menendez said the administration failed to meet the legal definition of an emergency and he vowed to work with legislators to counter the decision.

"The lives of millions of people depend on it," Menendez said.

Tensions between Iran and the US mounted this month, a year after Trump pulled the US out of the landmark 2015 nuclear deal. Many Democrats have expressed scepticism about the Iran threat, saying the Trump administration is blowing things out of proportion.

The Republican Foreign Relations Committee chairman, Senator Jim Risch, said on Friday he had received formal notification of the administration's intent to move forward with "a number of arms sales".

In a statement, Risch said: "I am reviewing and analysing the legal justification for this action and the associated implications."

'An end run around Congress'

The Trump administration's move comes as members of Congress continue to express concern over the president's handling of the US's strategic relationship with Saudi Arabia.

Earlier this year, Congress approved a resolution that would have ended US involvement in the Saudi-UAE war in Yemen. Trump vetoed the measure.

Several members of Congress, including many Republicans, have also expressed anger over the murder of Saudi writer Jamal Khashoggi, who was killed last year in Saudi Arabia's consulate in Istanbul, Turkey.

US intelligence agencies have concluded Saudi Crown Prince Mohammed bin Salman ordered the killing - a conclusion the kingdom denies.

"Rather than stand up against those who murdered Jamal Khashoggi and are working against US interests, the Trump administration decided to do an end run around the Congress and possibly the law," Menendez said.

Senator Chris Murphy said that Trump "is only using this loophole because he knows Congress would disapprove ... There is no new 'emergency' reason to sell bombs to the Saudis to drop in Yemen, and doing so only perpetuates the humanitarian crisis there."

Boon to defence industry

In documents sent to Congress, Pompeo listed a wide range of products and services that would be provided to the countries.

They include Raytheon precision-guided munitions (PGMs), support for Boeing Co F-15 aircraft, and Javelin anti-tank missiles, which are made by Raytheon and Lockheed Martin Corp.

Other companies that will benefit include General Electric, now cleared to sell engines for use in F-16 fighter jets operated by the UAE, and the US unit of French firm Thales, which was cleared to sell a fuzing system for Paveway IV precision-guided bombs to Britain and the UAE.

It will also likely be welcome news for Britain’s BAE Systems Plc and Europe’s Airbus, clearing the way for the installation of Paveway laser-guided bombs on European-built Eurofighter and Tornado fighter jets sold to Saudi Arabia, as well F-15 fighters built by Boeing.

Separately on Friday, Trump said he was deploying 1,500 additional US troops to the region to counter Iran, part of a major US pressure campaign to roll back Tehran's influence in the Middle East.