Turkish troops and allied Syrian rebels expelled the Islamic State group from the last strip of territory it controlled along the Syrian-Turkish Border on Sunday, effectively sealing the extremists’ self-styled caliphate off from the outside world, Turkey’s prime minister and a Syrian opposition group reported.

On Sunday, Syrian pro-government forces backed by airstrikes launched a wide offensive in the northern city of Aleppo,  capturing areas they lost last month and besieging rebel-held neighbourhoods, state media and opposition activists said.

Turkey-backed Free Syrian Army rebels have cleared the area between the northern Syrian border towns of Azaz and Jarablus, Turkey’s prime minister Binali Yildirim said.

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“From Azaz to Jarablus, 91 kilometers of our border has completely secured. All the terrorist organisations are pushed back, they are gone,” Yildirim said, speaking at a dinner with non-government organizations in the southeastern city of Diyarbakir.

The FSA’s advance shut down key supply lines used by IS to bring in foreign fighters, weapons and ammunition.

The Britain-based Syrian Observatory for Human Rights said IS “has lost its link with the outside world after losing all border areas” with Turkey.

It said the last two border villages that IS held were Mizab and Qadi Jarablus, which were taken this afternoon.

IS had occupied the border area even before it declared its self-styled caliphate in June 2014, and it used the Turkish border to bring in fighters from around the world.

The extremist group, which controls parts of Syria and Iraq, is now surrounded from all sides by hostile forces.

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The loss of its territory along the Turkish border follows a series of recent defeats for IS, including its expulsion from the central Iraqi city of Fallujah and its defeat in the former stronghold of Manbij in northern Syria.

Airstrikes by the US-led coalition have killed a number of the group’s most prominent founding members and leaders.

In a statement, Turkey’s armed forces said the “the Jarablus-Azaz line has been connected.”

Turkey has long pushed for a safe zone in Syria between these two towns, with a plan to house Syrian refugees there.

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Turkey hosts an estimated 3 million Syrian refugees, the highest number in the world.

Meanwhile, the recapture and return to siege of rebel-held parts of Aleppo dealt a major blow to insurgent groups. They have lost scores of fighters in recent weeks in the battle to open a corridor into the city and lift the government’s blockade.

After the government laid siege on Aleppo for the first time in July, the United Nations said that nearly 300,000 residents were trapped in rebel-held neighborhoods, making it the largest besieged area in war-torn Syria.