Tensions have been brewing between the U.S. and Iran since Iran's Islamic Revolution four decades ago, but the situation reached a boiling point last month after the U.S. claimed an increased threat from Iran, a year after pulling out of a multi-nation nuclear treaty with Tehran.
The rhetoric has simmered, and both sides have insisted they do not seek war. But concerns remain that the situation could quickly change and shoot past the boiling point.
One reason for continued worries is that Iran and the U.S. don't have any direct line of communication. It's become a national security dilemma that's left both sides vulnerable to misinterpreting each other's actions.
On Wednesday, Japanese Prime Minister Shinzo Abe traveled to Tehran -- the first time a sitting Japanese premier has visited the country in the 40 years since its Islamic Revolution -- to act as mediator between the two feuding nations. His trip was the highest-level diplomatic effort so far aimed at lowering the rhetoric as Iran appeared ready to break the 2015 nuclear deal.
Whether Abe will be successful in his efforts remains to be seen. Experts say that problems between the U.S. and Iran have intensified since a series of events left politicians and the international community worried the two nations were edging toward a military conflict.
Also, whether it's Iran's nuclear ambitions, conflicting goals in the Middle East or issues of human rights, the nations have continued to clash on numerous fronts over the last several decades. Here's an explanation of how relations took a turn for the worse and where things stand today.
-- What caused the recent flare-up in tensions?
The impetus for the most recent uptick in tensions, analysts say, was the Trump administration's decision to label Iran's Islamic Revolutionary Guard Corps as a foreign terrorist organization. In retaliation, Iranian lawmakers on April 8 designated U.S. forces in the Middle East as a terrorist group.
About a month later, President Donald Trump's hawkish national security adviser, John Bolton, announced the Pentagon would deploy the Abraham Lincoln Carrier Strike Group and Air Force B-52 bombers to the Persian Gulf. Bolton said the move was in response to "a number of troubling and escalatory indications" by Iranian security forces.
U.S. officials claimed they had intelligence that showed Iran's Islamic Revolutionary Guard Corps had put cruise missiles aboard small boats, threatening American naval ships in the Persian Gulf.