Syrian rebels backed by Turkish troops and tanks recaptured Isis' last major stronghold on the Syrian-Turkish border, inflicting yet another defeat on the militants rapidly dwindling "caliphate".
Rebel fighters and Turkish officials said the rebels had reached the centre of Jarabulus after encountering almost no resistance from Isis (Islamic State) fighters, who appeared to have fled ahead of the advancing forces. Photographs posted on social media showed rebels posing in front of government buildings in the town's central square.
The capture of Jarabulus deprives Isis of a crucial foothold on the Turkish border, used for funnelling foreign fighters and supplies, and is expected to help accelerate the militants' demise elsewhere across its self-proclaimed caliphate.
The offensive was spearheaded by Turkey, which sent tanks, troops and warplanes into Syria for the first time in the country's five-year-old war to help a force of hundreds of Syrian rebels.
The operation also includes US advisers, who are working from inside Turkey, while American surveillance aircraft are providing overflight intelligence and are poised to contribute US airstrikes if necessary, according to a senior Obama Administration official.
It coincided with a crucial visit to Ankara by US Vice-President Joe Biden, and it seemed intended to demonstrate that Turkey and the United States remain close allies in the war against Isis, notwithstanding tensions that have strained their relationship since a failed coup attempt last month.
The presence of Turkish troops in Syria will also add a new layer of complexity to the already massively complicated war, potentially pushing Turkey closer towards conflict with US-backed Syrian Kurds and perhaps the Syrian Government.
The Syrian Government condemned the Turkish incursion, describing it as a "blatant violation" of Syrian sovereignty.
Russia's Foreign Ministry said it was "deeply worried" by the US-backed Turkish incursion, citing the risk that it may cause civilian casualties.
The offensive against Isis fighters in Jarabulus, along the Euphrates River, began just hours before Biden arrived on a mission to repair the eroding US-Turkey relationship, which is considered crucial to the ongoing battle against Isis.
Nato-member Turkey in recent weeks has backed away from its traditional alliance with the West in favour of fresh ties with Russia. President Recep Tayyip Erdogan's pivot toward Moscow, where he visited President Vladimir Putin last week, comes less than a year after Turkish warplanes shot down a Russian fighter jet flying sorties over Syria, causing relations to spiral and pushing the two countries to the brink of war.
Erdogan and Putin remain on opposing sides of Syria's civil war, with Turkey backing Sunni Islamist rebels and Russia supporting Syrian President Bashar al-Assad. But Turkish officials have hinted that they would allow Russian fighter jets to use Incirlik Air Base - where US troops and aircraft are stationed - to launch bombing raids on Isis targets in Syria.
Turkey is also angered by America's support for US-backed Kurdish forces in Syria, which it sees as a threat to its territorial integrity. Turkey is home to roughly 14 million Kurds, including Kurdish militants who have waged a decades-old war for autonomy.
Turkey has vowed to prevent any further territorial gains by the Kurdish-led Syrian Democratic Forces (SDF), and the operation may be intended as much at halting their progress as recapturing territory from the Islamic State
The Kurdish People's Protection Units (YPG) in Syria also have proved an effective fighting force against the Isis, benefiting from US backing but also alarming officials in Ankara.
The capture of Jarabulus from Isis could blunt a parallel offensive by the US-backed YPG-dominated force that has been advancing against Isis militants farther to the south at the city of Manbij.
But the Obama Administration apparently has decided that it is more important to assuage Turkish sensitivities than to expand the Manbij offensive towards the north.