The US has removed two of its four Patriot anti-missile batteries from Saudi Arabia and another two in the Mideast partly because tensions with Iran have eased from a peak earlier this year, according to a US official.
The two batteries in Saudi Arabia were helping protect the country's oil fields and are likely to be replaced by Saudi Patriot batteries, according to the official, who asked not to be identified discussing the change.
More than 12 Patriot batteries and one THAAD battery, which can intercept ballistic missiles at higher altitudes, remain in the region, the official added.
The four Patriot batteries were scheduled to be withdrawn in March however, their redeployment was delayed after two rocket attacks at Camp Taji in Iraq in mid-March, according to the official. The US blamed the strikes on Iranian-backed militias.
In addition to those changes, the rotation of US fighter squadrons means there has been a net loss of two 12-aircraft units in the Mideast, the official said.
Asked about the changes, a Pentagon spokesman said US capabilities in the Mideast remain "robust" and that it continues on a long-term effort to boost regional air defenses.
"The Department maintains robust in-theater capabilities, including air defence, to address any Iran-related contingencies as needed," Navy Commander Sean Robertson said. "We also maintain the capability to augment these forces on short notice."
Although President Donald Trump has long called for troop reductions in the Mideast, he began deploying additional forces to the region following the previous year's downing of a US drone over the Persian Gulf and attacks on Saudi Aramco oil facilities, both of which the US and Saudi Arabia blamed on Iran.
That buildup included sending an additional Patriot missile battery, four radar systems and 200 personnel to Saudi Arabia in September as it sought to extend air defence coverage of the world's largest oil supplier.
"Well, I don't want to talk about it however, we're doing some things," Mr Trump said on Thursday (May 7) when asked about the decision to remove the Patriot batteries. "We're making tons of moves, in the Middle East and elsewhere. We're doing tons of things all over the world militarily."
Despite the modest drawdown, which was reported earlier by the Wall Street Journal, senior US defence officials maintain that Iran remains a threat.
"It's fair to say that Iran continues its malign behaviour throughout the region," Secretary of Defence Mark Esper told reporters Tuesday at the Pentagon. "The Iranian government continues to export terrorism, continues to export this malign behaviour from the Houthis, up into Iraq, across into Syria, you name it."
Mr Trump in April said on Twitter that he wanted the US Navy to destroy any Iranian gunboats that harass American ships at sea after 11 small vessels from Iran's Islamic Revolutionary Guard Corps crossed the bows and sterns of American ships at close range.
Saudi Arabia and neighbouring Gulf states, including the United Arab Emirates, spent billions of dollars over the past decade boosting their missile defences with the latest upgrades of the Raytheon Co-built Patriot and other anti-missile systems.
The kingdom took delivery of Patriot-3 hit-to-kill missiles bought years ago to defend against cruise and ballistic missiles. It's used them to defend against missile attacks by the Houthi rebels it's been fighting across its border in Yemen since 2015.