Amid rising tensions in the Gulf, Iran is pushing the boundaries to see how far it can go — but U.S. President Donald Trump has so far not been "compelled" to retaliate militarily, according to analysts.
That could change if Tehran crosses the"red line" — which may include deaths or injuries of American personnel, they said, warning of its dangers.
Tensions between the U.S. and Iran were already building up after Washington pulled out of a nuclear deal with the Islamic state.
Last Friday, Tehran seized a British-flagged tanker in the Strait of Hormuz — a major choke point for oil shipments — after the United Kingdom stopped an Iranian tanker several weeks ago for allegedly carrying crude oil to Syria, in an alleged sanctions violation.
Before the seizure, Iran shot down an unmanned U.S. drone in June, prompting the White House to consider responding militarily. But Trump called off the retaliatory attacks at the last minute, and instead, slapped Iran with "hard-hitting" new sanctions.
"President Trump has certainly telegraphed his marked aversion to a military conflict, but there still seem to be important redlines that, if crossed, could cause him to go down that path," said a report by RBC Capital Markets.
That red line, for Trump, would be any deaths or injuries of American soldiers, diplomats or citizens, said Henry Rome, an analyst for global macro politics at Eurasia Group.
"But because we have not seen that, the president has not felt compelled to retaliate," he told CNBC on Tuesday. "The Iranians have been trying to feel around to find out where this red line is."
"When (Iran) shot down the U.S. drone ... many folks thought that could be the start of conflict. But it became quite clear from the U.S. point of view, that because it was an unmanned vehicle, it would not trigger that red line," he said.
Nonetheless, Rome warned: "The risk of war is very significant and should not be understated."
Last week, Iranian Foreign Minister Mohammad Javad Zarif told NBC News that Tehran does not want a war and that the door to negotiations would be wide open if Trump lifts sanctions on Iran. The sanctions on Iranian oil, aimed at crippling the Islamic Republic's economy, came after the U.S. pulled out of a multilateral nuclear deal. The agreement, known as the Joint Comprehensive Program of Action, was made by Iran, the U.S. and five other countries.
Britain, one of the parties, has been trying to keep Iran in the nuclear agreement. Still, Iran has moved to enrich more uranium at higher levels — breaking that nuclear deal.
The RBC report said there are other triggers that could prompt the U.S. to take military action. They include a "serious ramp up" in Iranian nuclear activities, bringing the country closer — estimated to be about two to three months — to being able to assemble a "crude nuclear device."
A "major attack" on an American ally in the region that results in numerous casualties, could also prompt Washington to act, it added.
"For now, the Iranian escalations seem to be calibrated to raise the temperature but to avoid a full boil over (the) situation," the report said.
But Eurasia's Rome warned Iran is playing "a very dangerous game" by turning up temperatures.
By challenging the freedom of navigation in the Gulf, the rogue state is building leverage and showing what it can do if its demands aren't met, said Rome.
"Basically the Iranians are treading a very thin line. It's the same with their nuclear program, it's the same with their activities in the Gulf. They want to create enough trouble to try to bring folks onto their side ... but not turn them against them," he said.
"They're trying to turn up the temperature ever so slightly and in a calibrated way to try to force other countries to come to their side without provoking a sharp counter reaction. But it is inherently a very dangerous game," Rome concluded.
— CNBC's Patti Domm contributed to this report.