The U.S. military will begin putting observation posts in northern Syria to help Turkey secure its border from the threats wandering through the war-torn country.

The move could prevent skirmishes in areas near Turkey’s border from distracting U.S.-backed fighters from their mission to defeat the Islamic State. The buildup, though, could draw the ire of U.S. lawmakers, some of whom view the mission in Syria as drifting away from the original goal of defeating ISIS.

“This is a change, now," Defense Secretary Jim Mattis told reporters Wednesday at the Pentagon. “We are putting observation posts in several locations up along the northern Syrian border because we want to be the people who call the Turks and warn them if we see something coming out of an area that we’re operating in."

Mattis said this move was made in close consultation with Turkey, a NATO ally that has made several offensive operations into Syria over the past few years to deal with militant groups it says pose a threat.

“We are going to track any threat we can spot going up into Turkey,” Mattis said. "That means we’ll be talking to Turkish military across the border.”

The new observation posts won’t require additional troops, though, he added.

The observation posts will be “very clearly marked” for both day and night operations so Turkish forces know their locations, according to Mattis. The U.S. military also this month began joint patrols with uniformed Turkish troops, part of a road map for easing tensions in the region between the two NATO allies.

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“What this is designed to do is make sure that the people we have fighting down in the [Middle Euphrates River Valley] are not drawn off that fight and that we can crush what’s left of the geographic [ISIS] caliphate,” Mattis said.

ISIS is largely relegated to a pocket of land near the Syria-Iraq border. Fighting there has been exceptionally difficult, as it is one of the last places the terror group still holds territory, and they are determined not to lose it.

The U.S. has also had difficulties keeping one of its most lethal contingents of the Syrian Democratic Forces — the Kurdish YPG — from abandoning the fight against ISIS in order to head north where they clash with Turkish military and proxy forces.

Turkey and the Kurds have a long history of conflicts. Turkey considers YPG fighters an offshoot of the Kurdish PKK, a U.S. State Department-recognized terror group.

U.S. officials, meanwhile, have consistently praised the YPG for their role in winning back swaths of territory from ISIS, buoyed by U.S. air power.

“We do not say the YPG is the same as PKK,” Mattis said. “And the Syrian Democratic Forces, who have lost thousands of troops killed and wounded fighting ISIS, got distracted by the instability up around Afrin and Manbij [in northern Syria], so they were not staying fully focused.”

U.S. and Turkish soldiers discuss details during the first-ever combined joint patrol on Nov. 1, 2018, in Manbij, Syria. (Spc. Arnada Jones/Army)

The observation posts could play an important role in reigning in the clashes that erupt periodically between Turkish and Kurdish forces. However, the Pentagon’s Syria mission has also faced scrutiny in recent months from members of Congress, who view a prolonged buildup in the country as ill-advised.

A bipartisan group of legislators on the House Armed Services Committee questioned Pentagon officials about the war in Syria in late September.

Massachusetts Rep. Seth Moulton, a former Marine Corps infantry officer, raised concerns about using U.S. troops to take back towns and keep them separate from a united Syrian state in the long term, which he characterized as looking akin to “Medieval kingdoms."

The U.S. presence in Syria is situated close to Jordan near Al-Tanf, in Syria’s north at Manbij, along the country’s border with Iraq near Al Qaim and Abu Kamal, and in other portions of Syria’s northeast, where the U.S. military partners with the Syrian Democratic Forces.