One misstep by any side could see Middle East descend into bloody conflict
Even by the explosive standards of the Middle East, this is an incendiary moment.
One misstep, one miscalculation on any side, could see the region descend into bloody conflict.
The Americans have removed not just a formidable and feared enemy - they have struck at the heart of the Iranian regime.
Qassem Suleimani was the second most powerful man in the country. The head of the military's elite force.
Those astonishing images of his funeral procession in Tehran show that the Americans have united Iranians at a time when the internal opposition to their theocratic rules was growing.
And now, in a region that respects and understands strength, the blood-curdling rhetorical vows to take vengeance will have to be turned into action.
But the when, where and what of their response will have to be carefully calibrated.
They could seek to cripple the world's oil supplies in the Gulf. They could attack US bases in Iraq and beyond.
They might well avoid direct confrontation by calling on the network of fighters that is Suleimani's legacy.
In Lebanon, Hezbollah, funded and backed by Tehran, has already warned it will send US troops in the region home in body-bags.
Hezbollah is capable of striking Israel; though such a move would only come if the situation deteriorates ever further.
So far, Iran's most significant step has been to pull out of the international agreement that limits its nuclear programme.
That's not quite the provocation it might appear; that will depend on the level of uranium enrichment.
But the next military move is Tehran's to make. Will it goad President Trump into fulfilling his threat to hit Iran hard?
There is only a small window of opportunity to work on diplomatic solutions.
What is easier to see is the region being drawn into the one thing both sides say they want to avoid.
And that is war.