Bahrain Mirror- AFP: The White House announced a huge arms deal with Saudi Arabia on Saturday as President Donald Trump took his first steps on the world stage, looking to leave mounting troubles behind at home.

The $110 billion deal for Saudi purchases of US defence equipment and services came at the start of an eight-day foreign tour that will also take Trump to Jerusalem, the Vatican and meetings with leaders in Europe.

The US president was given a warm welcome in the oil-rich kingdom -- a mood in sharp contrast to Washington where pressure is building after fresh claims over his team's alleged links to Moscow.

Air Force One had barely taken off when it was announced late on Friday that James Comey, the former FBI chief fired by Trump, had agreed to testify publicly about Russian interference in the US elections.

Reports also emerged that Trump had called Comey "a nut job" and that the FBI had identified a senior White House official as a "significant person of interest" in its probe of Russian meddling.

The president and first lady Melania Trump were welcomed by Saudi King Salman as they disembarked at King Khalid International Airport in Riyadh on Saturday morning.

Trump and his wife, who dressed conservatively in black but did not cover her hair as Saudi women are required to do, walked side-by-side to the tarmac where they both shook hands with the 81-year-old king.

After a welcoming coffee ceremony, Trump and his entourage were brought to the royal court where the president was awarded the Collar of Abdulaziz Al Saud, Saudi Arabia's highest civilian honour.

The arms sale agreement was just one of a series of deals to be announced during the visit, with US conglomerate General Electric saying it had also signed agreements and memorandums of understanding worth $15 billion.

"This package of defence equipment and services support the long-term security of Saudi Arabia and the Gulf region in the face of Iranian threats," a White House official said in announcing the deal.

Trump held talks with Salman and was to meet the kingdom's two powerful crown princes on Saturday, before giving a speech on Islam to leaders of Muslim countries on Sunday.

For Riyadh the visit is an opportunity to rebuild ties with a key ally, strained under Trump's predecessor Barack Obama who Sunni Arab Gulf states suspected of a tilt towards their Shiite regional rival Iran.

A more muted focus on human rights should also please Washington's traditional Sunni Gulf allies, analysts say.

Shortly after arriving Trump took to Twitter to express his delight at being in the kingdom.

"Great to be in Riyadh, Saudi Arabia. Looking forward to the afternoon and evening ahead," Trump wrote.

Sunday's speech to dozens of Muslim leaders has been touted as a major event -- along the lines of a landmark address to the Islamic world given by Obama in Cairo in 2009.

The speech will be especially sensitive given tensions sparked by the Trump administration's attempted travel ban targeting several Muslim majority nations and accusations of anti-Islamic rhetoric on the campaign trail.

Trump wants Gulf states in particular to do more to tackle extremists such as the Islamic State jihadist group.

In return he is expected to take a harder line on Iran, where it was announced Saturday that President Hassan Rouhani had won a resounding re-election victory as voters overwhelmingly backed his efforts to reach out to the world.

Before departing, Trump tweeted he would be "strongly protecting American interests" on his trip.

While most US presidents make their first foreign trip to neighbouring Canada or Mexico, 70-year-old Trump has opted instead for the Middle East and Europe.

- Avalanche of revelations -

He travels to Israel and the Palestinian Territories on Monday and Tuesday, and then to the Vatican and to Brussels and Italy for NATO and G7 meetings.

The tour has been billed as a chance to visit places sacred to the three major monotheistic religions -- Islam, Judaism and Christianity.

But it is also fraught with peril for the real estate magnate, who is known to dislike lengthy travel.

The avalanche of revelations in the run-up to his departure has eroded Trump's standing at home.

On Friday, a report by The Washington Post that the probe into his campaign's Russia ties had identified a "significant person of interest" in the White House undercut Trump's insistence his election bid had nothing to do with the Kremlin.

The White House was rocked by another bombshell when reports emerged that Trump said his firing of "nut job" Comey had relieved "great pressure" on him due to the investigation.

The scandals have revived questions about his ability to strike a presidential tone with his foreign counterparts.

The first leg of the trip is likely to be the easiest -- Saudi leaders are keen to work with an administration they see as more in line with their goals.

The normally austere kingdom put on a major display for the visit, with the streets of Riyadh lined with US and Saudi flags and billboards featuring Trump and King Salman.

The next leg in Israel be more complicated, despite the history of warm ties between Trump and Prime Minister Benjamin Netanyahu.

The visit is already awash in controversy, from a row over Trump's planned visit to Jerusalem's Western Wall, the holiest prayer site for Jews, to his alleged disclosure of Israeli intelligence to Russian officials.

After meeting Netanyahu in Jerusalem, Trump will see Palestinian president Mahmud Abbas in Bethlehem, part of his efforts to revive the long-stagnant peace process.

On Tuesday Trump heads to Rome to meet with Pope Francis. The two men are at odds on everything from climate change to refugee policy, although the pontiff says he will give the US leader an open-minded hearing.

The president will then meet NATO members in Brussels and attend a G7 summit in the Sicilian town of Taormina.

These meetings -- including with new French President Emmanuel Macron -- will be closely watched for signs of whether Trump and traditional US allies in Europe can work together.