Like plucking a thread from a finely-woven Turkish rug, President Donald Trump’s precipitate announcement that the US was effectively abandoning a Kurdish militia could lead to an unravelling of that part of the Middle East in which various forces have collided since the Syrian civil war broke out in March 2011.

This is a humanitarian disaster in the making, even apart from its implications for America’s shaky reputation as a reliable ally across the region. Hasty US action taken without consultation with its allies, including principally the Kurds, after a phone call between Trump and Turkish President Recep Tayyip Erdogan risks resumption of bloody conflict in which tens of thousands of lives will be in peril. There is the additional risk of reigniting a wider Syrian civil war that is hardly contained in any case.

Turkey has been quick to take advantage of a White House announcement it was pulling back from north-eastern Syria, where US ally the Kurdish-led Syrian Democratic Forces (SDF) control territory in which 70,000 refugees are cooped up in a vast refugee settlement. The Turkish military has begun shelling SDF supply lines to Iraq in preparation for a move across the border to establish a so-called "safe zone" where it plans to relocate two million of the 3.6 million Syrian refugees on its soil. Adding vastly to complications, the SDF is detaining 10,000 to 12,000 Islamic State fighters in rudimentary prison camps across territory under its control. If this all falls apart, chaos would descend once again on that part of the Middle East where a US-Kurdish alliance had established relative calm.

In a raw geopolitical game in one of the most volatile corners of the world it is hard to exaggerate the degree of irresponsibility displayed by an American president in this instance. Under enormous criticism, particularly from his own Republican colleagues, Trump is resorting to bombast. “As I have stated strongly before, and just to reiterate, if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will total destroy and obliterate the Economy of Turkey (I’ve done before!),’’ Trump tweeted.

This intervention does not seem to have deterred Erdogan, who gives every appearance of being intent on pushing into north-east Syria in what will certainly result in a confrontation with the SDF.

Leading the charge against the Trump decision is his close ally, South Carolina senator Lindsey Graham. He has threatened to introduce a Senate resolution opposing the administration’s decision. Graham described Trump’s abandonment of US Kurdish allies who have helped defeat Islamic State as a “stain on America’s reputation".

What happens next to IS prisoners and refugees, including principally women and children from the collapsed Islamic State’s so-called caliphate, hardly bear contemplating.

In the face of such a Turkish move, the SDF would be hard put to hold sway against both Turkey’s military and Islamic State fighters seeking to take advantage of militia weakness in the absence of US support on the ground and in the air. Turkey views the main militia in the SDF, the Kurdish YPG, as cross-border allies of its own Kurdish PKK separatists. It regards the PKK as a terrorist organisation. It has been at war with the PKK for decades.

At the same time, Syrian forces of Bashar al-Assad, backed by Iran and Russia, would inevitably be poised to take advantage of chaos that might ensue to regain territory lost in the civil war. This is a highly destabilising scenario. In other words, Trump’s announcement could hardly portend a more worrisome outcome in a part of the world riven by years of conflict.

The US announcement also sends a disturbing signal to the wider Middle East that the Trump administration is intent on pulling back from its commitments in an unstable region. Confidence in American steadfastness is precarious in any case in the light of Trump’s repeated statement that America wants to remove itself from “endless’’ wars in the Middle East. “The United States was supposed to be in Syria for 30 days, that was many years ago. We stayed and got deeper and deeper into battle with no end in sight. WE WILL FIGHT WHERE IT IS TO OUR BENEFIT, AND ONLY FIGHT TO WIN,’’ he said in a Twitter message. Trump also attacked European allies over their failure to take back nationals among refugees held in SDF-supervised camps.

This is a situation ripe for Iran’s Revolutionary Guard Corps (IRGC) and Vladimir Putin’s Russia. The latter is seeking to reassert itself in a region that it regards as its own sphere of influence. Moscow’s support for Damascus is part of this regional power-play. Iran and Russia would not be displeased by signs of an apparent American lack of commitment, and nor would Islamist militants, like IS and al-Qaeda. These groups have been biding their time. None of America’s regional friends, including the Gulf monarchies and Israel, will draw any comfort at all from the Trump decision – if implemented – to head for the exits. By any standards, this is a mess of Trump’s own making.