The United States risks greater isolation and unpredictability in its anti-Iran drive after President Donald Trump opted to pull out of the Iran nuclear deal despite warnings from European allies, advisers and even some fellow Republicans, experts tell Reuters.
While Israel has warned of possible retaliation in its border areas with Syria, both as a result of alleged Israeli airstrikes in Syria on Iranian targets and Trump's Tuesday decision to pull out of the Iran nuclear accord, it is Saudi Arabia that may be the prime target for retaliation.
The U.S. has long accused Iran of escalating the civil war in Yemen and threatening to turn it into a broader regional conflict by supplying advanced weaponry, including missiles, to Houthi rebels who have fired rockets at targets in Saudi Arabia.
A U.S. intelligence official acknowledged concerns that Iran could, with some deniability, further assist the Houthis in Yemen as they target Iran's arch-rival Saudi Arabia. Saudi Arabia claimed Wednesday morning to have intercepted missiles fire at its capital from Yemen.
A successful missile strike from Yemen that kills large numbers of Saudis could trigger a major backlash, stoking risks of a broader regional war, experts say.
On the nuclear front, a collapse of the deal could also hasten the risk that Iran covertly attempts to reconstitute a nuclear program that once consumed U.S. intelligence officials and military planners.
Iran denies it has tried to build atomic weapons and says its nuclear program is for peaceful purposes.
While announcing the U.S. withdrawal from the Iran accord, Trump argued the deal provided Tehran generous sanctions relief without imposing tough enough limits on its nuclear program or other "sinister" activities.
But analysts said the decision could make it harder for the United States to rally European allies and others behind future action against Iran, which extends well beyond the nuclear arena to include threats by Tehran's proxies in Yemen, Syria, Iraq and even Afghanistan.
The U.S. move also creates a more unpredictable environment in the Middle East, in which Iran could choose to lash out against U.S. interests more openly or keep chipping away at them and extending its regional influence.
"We are now alone on a more dangerous path with fewer options," retired Army general Martin Dempsey, a former chairman of the U.S. military's Joint Chiefs of staff, wrote on Twitter.
Underscoring the tension in the region, the Israeli military went on high alert on Tuesday for a possible flare-up with neighboring Syria, which is allied to Iran.
"It's going to weaken the United States," said Nicholas Burns, the State Department's third-ranking official under Republican President George W. Bush, saying it would empower Iran's hardliners, further isolate the United States from Russia and China on Iran policy and vex European allies.
"This is going to have a profoundly negative impact on the willingness of the Europeans to work with us in the way that they have been for a very long time."
One U.S. official noted that a deterioration in the U.S.-Iran relationship would likely have negative effects across the border in neighboring Iraq, where voters are due to elect a new parliament on Saturday.
"As tension goes up in the U.S.-Iran relationship, it's always bad for the U.S.-Iraq relationship," said the U.S. official, speaking on condition of anonymity.
U.S. Defense Secretary Jim Mattis has accused Iran of "mucking around" in the parliamentary election, in which Prime Minister Haider al-Abadi is seeking another term after a successful, U.S.-backed war against Islamic State militants.
Mattis, who once spoke publicly of the need to abide by the Iran nuclear deal, has since tempered his remarks and told Congress it was an "imperfect arms control agreement" that needed to be fixed.
But Mattis, in private conversations, has also stressed the need to act with allies, given the threat he believes that Iran poses in the region, one U.S. official familiar with the conversations told Reuters.
In April 26 remarks to Congress, Mattis said: "We need to focus on what is in the best interest of Middle East stability and the threat that Iran poses." He said that threat extended beyond the nuclear program to "their support for terrorism" as well as their cyber threat.
A Western diplomat doubted the Iranians would retaliate against the United States in Syria because of the risk of Israeli retaliation, or in Iraq, where Tehran's influence has vastly expanded since the 2003 U.S. invasion that toppled former dictator Saddam Hussein.
"They have no interest in destabilizing Iraq. Things are not going so bad for them in Iraq. And in Syria, there is the big, big stick, the Israeli stick, and they feel that the stick is ready to fall," the diplomat said.
"They are not going to risk a war with Israel ... to punish the Americans."
Israel has traded blows with Iranian forces in Syria since February, stirring concern that major escalation could be looming.
The Israeli military said on Tuesday that after identifying "irregular activity" by Iranian forces in Syria, it instructed civic authorities on the Golan Heights to ready bomb shelters, deployed new defenses and mobilized some reservist forces.
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