Troops identified by Syrian Democratic forces as members of U.S. Special Operations are seen on May 25, 2016, near the village of Fatisah in the northern province of Raqqa (AFP/Getty Images).

MUNICH, Germany — As the fight against the Islamic State moves beyond its de facto capital in Raqqa, the Pentagon is readying itself for an increasingly complex battlefield in northern Syria, where U.S.-backed forces, pro-Syrian government troops and Russian jets will likely all be fighting near one another.

Speaking to reporters on his way to Germany on Monday to meet with European allies, Secretary of Defense Jim Mattis spoke broadly about the U.S. military’s future operations against the Islamic State in the Euphrates River Valley, adding that it will take “more precision” to stave off any incidents between the disparate forces operating there.

“You have to play this thing very carefully,” Mattis said. “The closer we get, the more complex it gets.”

Mattis also acknowledged that the U.S. would continue to supply Kurdish forces in the north with weapons despite objections by U.S. ally Turkey. “When they don’t need them anymore  we’ll replace them with what they do need,” he said.

The strip of the Euphrates River Valley that runs through northeastern Syria has turned into one of the last Islamic State redoubts following the group’s near-defeat in the Iraqi city of Mosul and the U.S.-led operation to encircle its stronghold in Raqqa. While the Pentagon has eyed the region as the next place to attack the militants, Syrian government forces and Iranian-backed militias have also made a concerted effort to move into the area.

To avoid the seemingly inevitable collision between U.S.-backed fighters and pro-Syrian government forces, including their respective air support, Mattis indicated that the Euphrates River Valley, would be carved up into “deconfliction” areas. The zones would be marked by easily identifiable parts of the river valley, such as towns and geographic features on the map, he said.

“As long as it’s worked out by the commanders and enough people know about it in sufficient time there are ways that have proven that we can do this,” Mattis said. The retired four-star Marine general suggested that with so many forces operating in the same area that deconfliction efforts would have to be worked out differently than they have in the past, though how exactly is unclear.

Currently, there are a number of communication lines between Russian and U.S. forces, including one that runs into the U.S.-led coalition’s main operations center in Qatar and another that connects the commander of U.S. forces in Iraq and Syria, Lt. Gen. Stephen Townsend, to his Russian counterpart in Syria.

“The deconfliction lines, through all of these contentious months that we’ve been through, have never gone down,” Mattis added.

The communication channels between the United States and Russia, Mattis said, have helped U.S. forces stay “focused” on fighting the Islamic State and have kept the United States from a widening role in the six-year-old conflict that has claimed hundreds of thousands of lives and displaced millions.

“We just refuse to get drawn into the Syrian Civil War,” Mattis said. “We try to end that through diplomatic means.”

Just hours after his remarks, however, the White House released a statement saying that it had reason to believe Syrian President Bashar al-Assad’s forces were preparing for a chemical weapons attack and that his military would “pay a heavy price” if it conducted any such strike.

In April, President Trump ordered a cruise missile strike in response to what Washington claimed was a gas attack carried out by Assad’s forces that killed nearly 90 people. Assad denied any such attack.

In addition to the White House threat, a spate of incidents in recent weeks — including the downing of a Syrian government jet and two Iranian-made drones by U.S. aircraft — appear to suggest the opposite of Mattis’s claims. The series of air attacks, taken in self-defense by U.S. forces, according to the Pentagon, occurred as pro-Assad forces threatened or approached U.S.-backed Syrian fighters.

Following the shooting down of the Syrian jet, Russia said it would treat U.S. aircraft west of the Euphrates as “targets,” but since the threats U.S. aircraft have continued to operate on both sides of the river without apparent incident.

One contingent of U.S.-backed Syrian fighters is located in the south near the Iraqi border, while the other group — called the Syrian Democratic Forces, or SDF — is fighting in the northern city of Raqqa.

The Syrian Democratic Forces, backed by U.S.-led air power and supplied with American weapons, has been a point of friction between the United States and Turkey, as the latter sees the group’s Kurdish arm, known as the YPG, as a direct extension of the Turkey-based Kurdistan Worker’s Party, or PKK.

The PKK is considered a terrorist organization by both the United States and Turkey and has waged an insurgency within Turkish borders off and on for years. The Turkish government is concerned that the U.S. arms and equipment given to the YPG will end up in the hands of the PKK.

To allay this fear, Mattis, according to a report in Reuters last week, indicated in a letter to his Turkish counterpart that the Pentagon would take back the weapons from the Kurdish fighters after the Raqqa campaign.

On Monday, while Mattis didn’t directly confirm the letter’s existence, he did say the Pentagon would “recover that sort of gear” after it’s no longer needed. When asked by a reporter if he envisioned the entirety of the group’s U.S.-supplied weapons would be taken from them following the end of the campaign against the Islamic State, Mattis said, “We’ll do what we can.”

Mattis’s remarks leave open the possibility that the SDF will likely continue to fight the Islamic State in northern Syria after the operation to retake Raqqa ends.