DUBAI - The United States is deploying troops in Saudi Arabia as tensions soar with its arch-rival Iran raising concerns over navigation in the Gulf's strategic Strait of Hormuz.
It will be the first deployment of its kind since 2003 when American forces withdrew from the kingdom after a 12-year presence and two US-led wars with Iraq that culminated with the toppling of dictator Saddam Hussein.
Is a new war looming in the region?
Is this preparation for war?
Separate statements from Riyadh and the US Central Command, or CENTCOM, say the Saudi deployment aims to ensure stability in the turbulent Gulf.
"Based on mutual cooperation between Saudi Arabia and the United States of America, and their desire to enhance everything that could preserve the security of the region and its stability... King Salman gave his approval to host American forces," the Saudi defense ministry said.
CENTCOM said the deployment "provides an additional deterrent, and ensures our ability to defend our forces and interests in the region from emergent, credible threats".
But for Andreas Krieg, a professor at King's College London, the troop movement "is part of posturing and the US trying to increase its military options in case of a strike on Iran".
Washington and Tehran have been locked in a standoff since May 2018, when US President Donald Trump withdrew from the 2015 nuclear accord with Iran and began ratcheting up sanctions against the Islamic republic.
Trump and his oil-rich Saudi ally have also accused Iran of attacking tankers and drones in the Gulf since last May.
Iran denies the charges and has threatened to close the Strait of Hormuz -- a chokepoint for around a third of the world's sea-borne oil -- if attacked.
Riyadh and Washington have not revealed the number of troops that will be deployed in the kingdom, which lies about 200 kilometers (125 miles) from Iranian shores.
But US media reports said 500 American troops will be based at the Prince Sultan military airbase, south of Riyadh.
"Five hundred US troops in Saudi Arabia are hardly a buildup, particularly when we are thinking about a war with Iran," said Krieg.
"These troops are there to prepare the Prince Sultan airbase for potential deployment of an air squadron," he added.
The base housed thousands of US troops and squadrons of jet fighters from 1991, starting with Operation Desert Storm after Iraq invaded Kuwait, to 2003 when the US-led invasion of Iraq toppled Saddam.
What is the message?
Analysts say the deployment is aimed at bolstering ties between Washington and Riyadh -- particularly military relations -- strained in the past year.
"The Saudis... are saying: if you stick with us we will stick with you," said James Dorsey, a researcher at Singapore's S. Rajaratnam School of International Studies.
"The Americans are trying to say: we have your back," he added.
Trump's administration has faced anger from lawmakers at home for not doing more to punish Saudi Arabia over last year's killing of Saudi journalist Jamal Khashoggi at the kingdom's consulate in Istanbul.
CENTCOM chief Kenneth McKenzie pledged to work "aggressively" to ensure maritime safety in the strategic Gulf waterway during a visit Thursday to Prince Sultan airbase.
The visit came a day after the US House of Representatives voted to block $8.1 billion in arms sales to the kingdom and other allies, in a move likely to be vetoed by Trump.
There has been growing outrage in the US, and around the world, over American arms sales to Saudi Arabia, with critics saying they are being used for its offensive in Yemen.
The UN says the Yemen conflict is the world's worst humanitarian crisis.
Is MBS a reliable partner?
Despite the criticism, Trump has repeatedly hailed Saudi Arabia's powerful crown prince, Mohammed bin Salman, who is also the kingdom's defense minister.
For the crown prince, also known by the acronym MBS, the deployment "is about showing that the US is still an important security guarantor and committed to Saudi security", said Krieg.
MBS, he said, has long been trying to divert some US troops from Al Udeid airbase in Qatar, home to Washington's largest Middle East military base.
"It is important for MBS to get some US assets to show that he is relevant as a security partner for Washington," said Krieg.
Around 10,000 US troops are deployed in Al Udeid, from among some 35,000 stationed in Gulf states including Kuwait and Bahrain, the latter being the home base of the US Fifth Fleet.
Al Udeid was set up in 2005 when the US was looking for a new airbase in the region after it pulled troops out of Saudi Arabia.
Saudi Arabia and its allies cut relations with Qatar in 2017 over Doha's alleged support for Iran and Islamist movements -- charges Qatar staunchly denies.