ISTANBUL — Turkey’s decision to launch a surprise military operation into Syria this weekend may be a sign that it’s bracing for backlash from the ISIS militants who control long stretches of the porous, 565-mile border between the two countries.

Late on Saturday, the Turkish military sent a column of tanks and troops to the Aleppo countryside, where Turkish soldiers have spent the civil war keeping guard at an historic tomb. A 1921 agreement gave Turkey control of the shrine to Suleyman Shah, grandfather of the founder of the Ottoman Empire — a small piece of Turkey located 20 miles into Syria. But ISIS’s presence in the area made the site a microcosm of Turkey’s vulnerability to blowback from the conflict next door.

The operation was a preemptive move to get the soldiers at the shrine out of harm’s way. Turkish forces removed the remains and destroyed the buildings that housed them without firing a shot, government officials said. A replacement shrine is being built on Syrian territory closer the border. Photos from the operation showed soldiers solemnly raising a Turkish flag there in the night.

The move came without warning — and the government has been vague about what sparked it. It also came on the heels of Turkey’s announcement that it had reached a deal, after months of negotiations, to host a U.S. train-and-equip program for Syrian rebels fighting ISIS. The Turkish government has been reluctant to support the U.S.-led coalition against ISIS too aggressively because it fears reprisals from the militants. Some analysts call Turkey’s balancing act with ISIS a “cold war” — and say it may be warming up.

“I think the dynamics of this cold war have shifted,” said Soner Cagaptay, who heads the Turkish Research Program at the Washington Institute for Near East Policy. “And the Suleyman Shah tomb was an emblematic ground where the Turkey-ISIS cold war played out.”

Cagaptay said Turkey likely worried that the train-and-equip deal would make it more of a target for ISIS — putting the troops at the tomb at additional risk. Discussions with the U.S. are also ongoing over the use of the Incirlik air base near Adana to assist with coalition airstrikes. And though Turkey remains a key transit point for ISIS fighters, it has announced crackdowns on the group of late. The government claimed recently that it has deported dozens of foreign ISIS fighters since January and barred some 10,000 people from entering the country for suspected ISIS links.

Turkey is not one of ISIS’s top enemies, Cagaptay said — it sits down the list from the group’s rivals in Iraq and Syria and governments in the West. But ISIS’s longstanding presence in Turkey and across the border increases the threat. “ISIS has at this point, unfortunately, a pretty good understanding of the [vulnerabilities] in the Turkish security system and how to exploit them,” Cagaptay said. “It’s hard to say whether it will be this month, next month, or next year, but at some point the cold war with ISIS will end.”

A Western diplomat based in Turkey cautioned that there is no “sea change” in Turkish policy on the horizon. It still has a long way to go in cracking down on ISIS, from targeting its infrastructure to making more arrests. “I don’t think there has been a significant shift. They’re still very focused on the regime,” the diplomat said, speaking on condition of anonymity because he wasn’t authorized to discuss the subject with the press.

The ISIS threat against Turkey came into stark relief this summer, when the group overran the Iraqi city of Mosul and took 49 people hostage from the Turkish consulate there. The hostages spent three months in captivity before the Turkish government secured their release — and the potential for a crisis at the tomb called their plight to mind. “Clearly Turkey is a target,” the Western diplomat said, adding that the tomb’s evacuation “allows them a little more space to breathe.”

For much of Syria’s civil war, Turkey turned a blind eye to extremists passing through its borders, including foreign jihadis, hoping these fighters would help to speed the downfall of the Assad regime. That allowed the extremists to plant roots on either side of the border, establishing sleeper cells and smuggling routes in Turkey along the way.

The threat of an ISIS attack has tempered Turkey’s response to the extremist group — and in turn, ISIS may be keen to avoid provoking the powerful NATO state. But all it takes is one flare-up for the détente to break down, said Jonathan Schanzer, an analyst at the Foundation for Defense of Democracies in Washington, DC. “This is a very precarious balancing act,” he said. “And it’s not sustainable.”