WASHINGTON (REUTERS) - President Donald Trump on Tuesday (March 20) praised US defence sales to Saudi Arabia as a boost to American jobs, even as lawmakers criticised Riyadh's role in the war in Yemen where a humanitarian crisis has unfolded.

In Oval Office talks, Trump and Saudi Crown Prince Mohammed bin Salman discussed an agreement last year for US$200 billion (S$260 billion) worth of Saudi investments with the United States, including large purchases of US military equipment.

Trump said the military sales contributed to the creation of 40,000 American jobs.

The talks were part of the first visit by the 32-year-old prince to the United States since he became the heir apparent last year to succeed King Salman.

Trump produced charts to show the depth of Saudi purchases of US military hardware, ranging from ships to missile defence to planes and fighting vehicles.

"Saudi Arabia is a very wealthy nation, and they're going to give the United States some of that wealth, hopefully, in the form of jobs, in the form of the purchase of the finest military equipment anywhere in the world," he told reporters.

But as they talked, US senators debated a resolution seeking an end to US support for Saudi Arabia's campaign in Yemen's civil war. Some members of Congress have been critical of the Saudi campaign, particularly the humanitarian situation and civilian casualties.

A Saudi-led coalition is fighting to counter the influence of Iran, an ally of the Houthi militia, which denies any help from Teheran and say it is fighting a revolution against corrupt politicians and Gulf powers in thrall to the West.

When the crown prince visited London earlier this month, Saudi Arabia and Britain signed a letter of intent to finalise talks on a multi-billion-pound order for 48 Typhoon fighter jets. Thousands of demonstrators protested outside the office of British Prime Minister Theresa May about the war in Yemen.

PRINCE'S RAPID RISE

Prince Mohammed capped his rapid rise to power last June by replacing his elder cousin Prince Mohammed bin Nayef, who had close relationships with US intelligence and defence circles, as crown prince. He is likely to rule for many decades if he succeeds his father.

Trump praised the king's move to elevate Mohammed and called US-Saudi ties strong as ever.

"I thought your father made a very wise decision. And I miss your father - a special man," he said. King Salman is slated to visit the United States later this year.

Though the prince has won Western plaudits for seeking to ease Saudi Arabia's reliance on oil, tackle chronic corruption and reform the conservative Sunni Muslim kingdom, the severity and secrecy of an anti-corruption crackdown last November has unnerved some investors.

The crown prince, in a rare foray into speaking English, said on Tuesday the Saudi pledge for US$200 billion in investments will end up at US$400 billion when fully implemented. He said a 10-year window for implementing the deal was already under way.

"This is a signal that there (are) a lot of things (that) could be tackled in the close future and more opportunities. And that's why we are here today, to be sure that we've tackled all the opportunities and achieve it and also get rid of all the threats facing our both countries," he said.

The two leaders were also expected to discuss tensions with Iran, Riyadh's regional arch-rival and a country Trump has repeatedly criticised for its expansionist policies in the Middle East.

He is on a public relations blitz while travelling in the United States, with stops in New York, Boston, Seattle, Los Angeles, San Francisco and Houston.

Trump and the crown prince underscored the strength of US-Saudi ties which suffered under the Obama administration. Saudi Arabia, a decades-long US ally, felt neglected by president Barack Obama's pursuit of a 2015 nuclear deal with Iran, Riyadh's regional rival.

Both Trump and the crown prince want to constrain Iran's rising influence in the Middle East. Saudi Arabia on Monday called the Iran nuclear deal a "flawed agreement," and Trump has made clear he plans to exit the agreement unless changes are made to it.

"We're going to see what happens," Trump said.

"But Iran has not been treating that part of the world or the world itself appropriately. A lot of bad things are happening in Iran. The deal is coming up in one month and we'll see what happens."

The prince is also due to have dinner with Jared Kushner, Trump's senior adviser and son-in-law, along with Jason Greenblatt, the two point men in the Trump administration overseeing Middle East peace efforts.

Crown Prince Mohammed and Kushner have forged a close relationship, which has at times come under criticism in Washington for circumventing normal diplomatic channels.