The United States has denied any intention to attack. But the public refusals of two allies to help could affect U.S. military options or require shifting of resources if tensions did seriously escalate.
Qatar -- home to 6,500 U.S. troops and the enormous al-Udeid Air Base, headquarters of all American air operations in the Middle East -- said earlier this month it would not permit an attack on Iran from its soil.
The Gulf Cooperation Council, a loose alliance of Kuwait, Qatar, Oman, Saudi Arabia, Bahrain and the Emirates, has called on all its members not to support any U.S. action against Iran.
The United States has close to 40,000 troops in the Gulf, including 25,000 in Kuwait, 3,000 in Bahrain, 1,300 in the United Arab Emirates and a few hundred in Oman and Saudi Arabia, according to figures from the Dubai-based Gulf Research Center.
Gulf Arab nations are increasingly uneasy with the United States' tough stance against Iran, fearing any outbreak of hostilities could bring Iranian retaliation. All lie within distance of Iranian missiles.
Also, Iran has booming trade and tourism links and full diplomatic ties with the Emirates and most Gulf countries.
On Wednesday, the U.S. Navy wrapped up its largest show of force in the Gulf since the 2003 invasion of Iraq, with 15 ships, 125 aircraft and 13,000 sailors in an exercise a few dozen miles off Iran's coast.
The maneuvers were meant to show "the commitment of the U.S. to stability and security in the region," said Rear Adm. Kevin Quinn, commander of Strike Group Three -- which includes the USS John C. Stennis.
Navy Lt. Cmdr. Charlie Brown said the U.S. Gulf maneuvers were defensive in nature, aimed at keeping open the sea lanes that carry two-fifths of the world's oil shipments.
"We're not looking for any kind of confrontation with Iran," Brown said. "The purpose of the exercise is to ensure that no one miscalculates about our commitment to security and stability in the Gulf."
But some U.S. allies were clearly aiming to make it clear they don't want to be caught in the middle if the situation escalates.
"We have assured the brothers in Iran ... that we are not a party in its dispute with the United States," said United Arab Emirates Sheikh Khalifa bin Zayed Al Nahyana in a statement carried on the Emirates news agency WAM. "We will not allow any force to use our territories for military, security and espionage activities against Iran."
The Emirates "refuses to use its territorial lands, air or waters for aggression against any other country," Khalifa said.
That could prevent the U.S. Air Force from flying intelligence missions over Iran with its squadron of U-2 and Global Hawk spy planes based at al-Dhafra Air Base near the Emirates capital, Abu Dhabi.
The U.S. Air Force said Wednesday it had not altered air operations in response to Sheik Khalifa's statement.
Air Force Lt. Col. Mike Pierson, based in Qatar, declined to say whether U-2s were flying missions over Iran, but said the Air Force operated only in international airspace or over countries that had granted permission.
In the run-up to the U.S.-led invasion of Iraq in 2003, Turkey denied access to Turkish territory, forcing U.S. military planners to adjust their plans and to forgo opening a northern front. The refusal ushered in a tense period in Turkish-American relations.