GAZIANTEP, Turkey — Under pressure from its allies in the West, Turkey has made it harder for would-be jihadists to slip across the border and join the ranks of the Islamic State group at its base in northern Syria.

But it has been unable — or unwilling — to halt the flow as the group, also called ISIS or ISIL, continues to replenish forces depleted in battle.

Smugglers from border villages who have long earned a living ferrying pistachios, sugar, cigarettes and fuel across the border say they are compelled by the Islamic State to traffic in jihadists, under the threat of death or the end of their livelihoods. Sometimes they receive a late-night phone call from an ISIS commander inside Syria directing them to receive a recruit at a luxury hotel in this city to escort across the border.

“Things have become more difficult because Turkey has stricter procedures on the border,” one smuggler who gave only his first name, Mustafa, said in an interview at a cafe in Kilis, a border town.