ON THE TURKEY-SYRIA BORDER — Come nightfall, a bucolic farming village begins to buzz with unusual activity. Shadowy figures emerge from olive groves, clutching small suitcases. Cars crowd the winding rural road collecting and discharging passengers. Farmers step onto their porches, ready to offer a bed for the night to Syrians who have hiked across one of the countless illegal crossing points along Turkey’s 550-mile border with their country.

On Wednesday, Turkey closed all of its legal border posts after Syrian rebels seized control of several crossings on the Syrian side. The move was prompted in part by concerns that Islamic extremists may have overrun at least one of the Syrian posts, at Bab al-Hawa, after a video posted online showed jihadi fighters there declaring they had established an “Islamic state.”

Turkish officials said that the closure would affect only Turks traveling to Syria and that Syrian refugees would still be allowed into Turkey.

But refugees do not use the official crossings. Nor do the rebels, arms smugglers, defectors and war wounded who have swarmed into southern Turkey in recent months, transforming one of the sleepiest parts of the country into a nerve center for the Syrian revolution.

Syria’s other borders, with Iraq, Lebanon and Jordan, are witnessing similar activity on a lesser scale. But it is in Turkey, whose government long ago embraced calls for the ouster of Syrian President Bashar al-Assad, that the Syrian rebels have found the warmest welcome.

“We must take care of them because they are our brothers and sisters,” said Suphi Atan, a spokesman for Turkey’s Foreign Ministry in the south, referring to the 43,000 Syrian refugees who are being housed in refugee camps dotting the border.

Far deeper role

Turkey’s role in the revolt goes far deeper than helping refugees, though to what extent it is actively aiding a war that has spun beyond the reach of world diplomacy is unclear. Turkey seems to be groping for a strategy to address the unfolding chaos on its doorstep, said Hugh Pope of the International Crisis Group in Istanbul.

“Turkey wants to have a say in what happens in Syria,” he said. “But I’m not sure it’s got any easy answers to what is going on. This is all new and unexpected for Turkey.”

What is clear is that the Syrian conflict has already reached deep into Turkey. The quaint and ancient city of Antakya, the preferred destination for most Syrians crossing the border, pulses with the intrigue and gossip of the war next door.

Free Syrian Army fighters stride through its narrow streets, sunburned and sweaty from the battlefield, hoping to meet benefactors to provide them with money and arms.

Salafi Muslims, who have come to offer help from the countries of the Persian Gulf region, huddle over kebabs, their long beards and robes conspicuous in secularist Turkey.

Men who identify themselves as representatives of rebel battalions rent cheap hotel rooms and apartments, swelling the population of a city, once part of Syria, where many still speak Arabic as their native tongue.