GAZIANTEP, Turkey — Kurdish fighters claimed to be closing in on Islamic State extremists holed up in a strategic Syrian frontier town Monday as Turkey was hit with a new influx of terrified civilians fleeing the fighting.

The developments came one day after thousands of desperate refugees cut a border fence and flooded through.

Video posted on social media by a pro-Kurdish group appeared to show columns of Kurdish fighters marching on the eastern fringes of the border town, Tel Abyad, and snipers dug in behind trenches firing on Islamic State positions. Kurdish commanders said they had seized a key road that would have allowed Islamic State militants to rush reinforcements from their de facto capital of Raqaa, Syria.

“Our forces are trying to break Islamic State defensive lines,” using artillery, heavy machine guns and sniper fire, said Shervan Derwish, spokesperson for the Euphrates Volcano coalition, a coalition of Kurdish fighters and allied Syrian rebel groups.

Islamic State fighters responded with at least one suicide car bomb, while the Kurds closing in on the town from the west sought to clear a large number of land mines left by the retreating extremists, said Derwish, reached by cellphone just south of Tal Abyad on Monday.

Since early May, a coalition of the Kurdish fighters, known as the Peoples’ Protection Units, or YPG, and Free Syrian Army units operating under the Euphrates Volcano umbrella group, have harried Islamic State extremists in the region, driving them from hundreds of villages. The sweep – an advance on Tal Abyad from both the east and west – has given the Kurds control over a large expanse of territory along the 550-mile Turkey-Syria border.

Tal Abyad, 50 miles north of Raqqa, is a key Islamic State resupply and oil-smuggling hub. Extremists took control of the town some 17 months ago during a round of internecine fighting among rebel groups.

The recent battles have triggered further mass displacement in Syria, with Turkish officials estimating some 16,500 new arrivals over the past two weeks. Turkish authorities on Monday granted permission for 400 more people to enter, local media reported. A Reuters photographer at the border estimated another 5,000 people managed to make their way into Turkey a day after a chaotic border scrum saw thousands of refugees cross into the Turkish frontier town of Akcakale.

Turkey’s state-run Anadolu News Agency posted video showing forlorn and frightened refugees pushing their way through a gap in the barrier clutching crying infants and dusty sacks filled with possessions, but Monday’s exodus appeared more orderly than the previous day’s, with soldiers helping people through a narrow opening.

Turkey is struggling to cope with an estimated 2 million Syrian refugees, at a cost of billions of dollars, and routinely appeals for greater support from Western countries. Turkish media on Monday quoted Deputy Prime Minister Numan Kurtulmus as saying the new wave could bring an additional 100,000.

The U.S.-led coalition has provided air support for the Kurdish advance, repeatedly striking Islamic State fighting positions and tactical units. Turkish officials suggested that those airstrikes had triggered the mass displacement, but the U.S. Embassy in Ankara defended the American strategy, saying militant positions and not civilians were being targeted.

The coalition’s support for the Kurds has angered Ankara, with President Recep Tayyip Erdogan claiming the U.S. may inadvertently “pave the way for a structure which could threaten our border,” according to the local Daily Sabah newspaper. The latest refugee influx comes at a delicate moment politically for Turkey, just over a week after a pro-Kurdish party scored an electoral success that will allow it to enter Parliament for the first time.

That gain came at the expense of the ruling AKP, or Justice and Development Party, which Erdogan co-founded and had hoped to propel to a two-thirds parliamentary majority that would grant his presidency great powers. Instead, the party now lacks the seats to rule alone and is being forced to seek coalition partners, with the possibility of new elections on the horizon if no new government can be cobbled together.

The Syrian Kurdish forces are closely linked to an insurgent group, the Kurdistan Workers’ Party, known in Turkey as the PKK. That group has waged a three-decade insurgency against the Turkish state at a cost of 40,000 lives. The PKK is considered a terrorist group by Turkey and the U.S.