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 Sunday 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.
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 U.S.-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. 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. The city has been contested since the summer of 2012.
Sunday's push follows a month after insurgents captured several military academies south of Aleppo and opened a corridor into opposition-held parts of Syria's largest city and onetime commercial center. Since then, government forces and their allies have been trying to recapture the area.
State TV quoted an unnamed military official as saying that troops are now in full control of the military academies south of Aleppo and are "chasing the remnant of terrorists." It added that all roads linking rebel-held eastern Aleppo with opposition areas outside the city "have been cut."
The Observatory confirmed these gains. "The (rebel-held) neighborhoods are under siege again," said the Observatory's chief, Rami Abdurrahman, by telephone. "The whole areas are under complete siege."
Turkey has launched two incursions into Syria since Aug. 24 in an operation designed to drive IS away from the border and prevent the advance of U.S.-backed Kurdish forces, which are also battling the extremist group.
Turkish Prime Minister Binali Yildirim on Sunday defended his country's intervention in Syria, pointing to their long shared border. "We are there to protect our borders, ensure the safety of our citizens' lives and property, and to protect the territorial integrity of Syria," Yildirim said in Diyarbakir.
Turkey has also said it will not allow Syrian Kurds to unite their "cantons," the regions under their control in northern Syria, which have emerged as autonomous zones during the civil war. Turkish President Recep Tayyip Erdogan said in a joint press conference with U.S. president Barack Obama in China that "our wish is that a terror corridor does not form on our southern border."
Turkey views the Kurds as a threat and the Turkey-backed forces have clashed with them outside Jarablus.
In an emailed press statement, Turkey's military said the FSA have taken 20 villages from IS, adding that the Turkish army struck 83 Islamic State group targets. Since the Turkish operation began on Aug. 24, the army says it has hit 383 targets with 1,599 rounds.
Bilginsoy reported from Istanbul. Associated Press writers Albert Aji in Damascus, Syria and Neyran Elden in Istanbul contributed to this report.