The International Institute for Strategic Studies said Tehran has established a regional network of some 200,000 fighters.
The energy secretary said Iran "could pay a very dear price economically" but added that Trump is "not interested in going to war."
What's the difference between 10,000 people being killed in air strikes, and a bunch of missiles taking out an oil processing facility for a few days? Money.
Russian Foreign Ministry spokeswoman Maria Zakharova also suggested the U.S. strategy in the Middle East is collapsing.
The White House has been considering how to respond to the weekend's attacks on Saudi oil infrastructure, which both Washington and Riyadh are blaming on Iran.
From North Korea to Venezuela, the "Art of the Deal" seems to have eluded the president. The recent attack on Saudi oil infrastructure, however, gives him a chance to shine through.
Retired Admiral William McRaven said the president's team must draw on their expertise to provide Trump with a range of options to respond to the attacks on Saudi Arabia.
President Trump is stuck between a rock and a hard place: he can't ignore an attack on a major ally and on the global oil market, but a military response, even of the "proportionate" variety, risks escalating the conflict.
The U.S. has yet to provide evidence to back up claims it was Iran, not Yemen's Houthi movement that was behind an attack on Saudi Arabia's oil facilities.
After a ruling in June 2019 barring arms exports to Saudi Arabia that could be used in Yemen, UK Secretary of State for International Trade apologized for two breaches.
The Houthis have claimed responsibility for Saturday's attack, but the U.S. has suggested that Iran is ultimately to blame.
"What if this whole thing goes south?" Kennedy asked during a segment of Fox News Outnumbered on Monday.
The Democratic presidential candidate criticized the president after he said he was "waiting to hear" from Saudi Arabia before acting in regards to the weekend Aramco drone attack.
"There's a vacuum of leadership inside the White House," the former White House communications director said.
"This is why it's so important to have a president who isn't a typical politician," the senior White House counselor said.
"Such [American] comments and measures are more akin to the plots hatched by secret and intelligence services for damaging the image of a state to prepare the ground for a series of [hostile] measures," the Iranian Foreign Ministry said.
Yemen's Iran-backed Houthi rebels claimed responsibility for drone attacks at the world's largest oil processing facility in Saudi Arabia, military and government spokespersons said Saturday.
In Yemen and beyond, these inhumane weapons serve virtually no military purpose and kill indiscriminately.
"There's a lot of money that historically has flowed from Gulf state individuals to the Trump family fortune," Senator Chris Murphy said, "and that has to be part of the explanation as to why they continue to bend over backwards to try to make the Saudis happy."
Senator Bob Menendez said he was "disappointed, but not surprised, that the Trump administration has failed once again to prioritize our long-term national security interests or stand up for human rights."
A Palo Alto man has been charged with felony vandalism after spray-painting the date of a school bus bombing that killed 44 children in Yemen on the campus of weapons manufacturer and defense contractor Lockheed Martin, who supplied the bomb.
"Egyptian withdrawal is a huge blow to the Arab NATO idea," one expert said. "The Arab NATO will properly die not far in the future."
The Trump administration admitted it had made seven approvals for the sharing of technological information with Saudi Arabia without telling Congress.
"Saudi Arabia has engaged in acts that are simply not acceptable," Republican Senator Jim Risch said.
American-made weapons were likely used in at least 25 unlawful attacks on civilians between April 2015 and April 2018, according to a new report by human rights groups.
The U.S. has been accused alongside Saudi Arabia of violating end user agreements to illicitly transfer weapons to insurgents in Syria.
President Donald Trump ignored a deadline to provide more answers on the Saudi crown prince's alleged role in the killing of Jamal Khashoggi. Now senators are coming after him.
Netflix said it removed the episode after receiving "a valid legal request—and to comply with local law."
The president offered his "Thanks to Saudi A!" for agreeing to rebuild Syria, but the details of the arrangement were not made clear.