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Syria's messy war is becoming even messier. On Tuesday, pro-regime militias reportedly moved into the embattled enclave of Afrin, which is under siege from Turkish forces who invaded Syria last month. The regime units appeared to be reinforcing Syrian Kurdish factions that have controlled the area near the Turkish border, much to the frustration of Ankara.

As I wrote during the early days of the Turkish incursion, the battles in Afrin risk a wider conflagration. The main Syrian Kurdish armed group, known as the YPG, is seen by Turkey as a direct proxy of the outlawed Kurdistan Worker's Party, or PKK, which operates inside Turkey and is considered a terrorist organization by Ankara and Washington. But the United States supports the YPG, depending on its fighters to help combat the jihadist Islamic State. Washington's complicated role in the war — as well as its decision to avoid becoming deeply involved in the clashes in Afrin — compelled the Syrian Kurdish militias to turn to President Bashar al-Assad for help.

“The Syrian government responded to the call of duty and sent military units on Tuesday, and they will be positioned along the border and take part in defending the unity and border of the Syrian territory,” YPG spokesman Nouri Mahmoud told reporters Tuesday.

Meanwhile, Turkish President Recep Tayyip Erdogan said Turkey would begin a heavy assault on the city center of Afrin in coming days. He described the Syrian government's move as the work of “terrorists” and claimed Turkish artillery had driven the pro-Assad forces back. Syrian sources claim that the barrage only briefly stalled the advance of the pro-Assad forces.

Shells fell near Afrin where militias allied with the Syrian government gathered on February 20 in a show of force against the Turkish offensive. (Point Agency)

The convoy's arrival is yet another geopolitical twist in a war that is growing ever more complicated. The pro-Assad militias that supposedly came to the Syrian Kurds' rescue probably had another set of allegiances: “The fighters arriving ... appeared to be from a network of Iran-backed units that have often bolstered the efforts of Assad’s military,” my colleague Louisa Loveluck reported.

If that is the case, we are seeing Turkey and its rebel allies potentially squaring off against pro-Assad militias that are linked to Iran and are operating in tandem with Syrian Kurdish units friendly with the United States — which opposes both the Assad government and Iran's presence in Syria. It is the sort of bewildering entanglement that characterizes the ruinous seven-year conflict, its constellation of warring parties and their tangled sets of interests.

From the Iranian perspective, the Turkish operation in Afrin was unwelcome. Iranian leaders, including President Hassan Rouhani, denounced the invasion, which soured recent talks held between Russia, Turkey and Iran over Syria's political future. According to the Middle East affairs website Al-Monitor, Iranian officials have pressed their Turkish counterparts to avoid a messy war of attrition in Syria.

“Turkey hoped that it would move into Afrin and its ... partners would look the other way. Ankara thought it got its wish when Russia, which controls the skies over Afrin, finally gave the green light to the Turkish military incursion into the Kurdish enclave,” wrote Gonul Tol, a fellow at the Middle East Institute in Washington. “But the recent developments on the ground suggest the way forward might not be as smooth and the partnership with Russia and Iran might not be as strong as Ankara had hoped.”

Outside Afrin, the Syrian chessboard is no less crowded. Rebel Islamist groups in nearby Idlib province are battling each other while also partnering with Turkish forces against the Syrian regime and its allies. The American air war in Syria, primarily directed at the Islamic State, has also led to the deaths of Russian mercenaries. The Assad government, with Russian support, continues to mercilessly pound rebel-held areas. And Israel, alarmed at Iran's entrenched presence in Syria, recently carried out airstrikes on suspected Iranian positions. Israeli officials openly talk about the prospect of entering a more intense regional war.

The hard reality for Ankara is that Turkey has few good options. Rising anti-American sentiment in Turkey, combined with U.S. support for the YPG, has placed the United States somewhat at odds with its NATO ally. No one else looks poised to step in. “Neither Russia nor Iran — both of whom Turkish politicians sometimes tout as potential replacements for the United States — seem terribly eager to accommodate Turkish interests,” wrote Nicholas Danforth, a Turkey expert at the Bipartisan Policy Center in Washington.

Indeed, there is a growing chorus in Washington to stop accommodating Ankara's agenda. “Nobody wants a violent rupture with Turkey,” wrote Washington Post columnist David Ignatius. “But seven years into the catastrophic Syrian war, observers need to admit some ground truths: The Turks allowed thousands of foreign radical Islamists to flow into Syria and create bases from which they threatened Europe and the United States; these terrorists would still be in their capital of Raqqa, planning attacks, if the United States hadn’t partnered with the Kurdish-led ... militia that Turkey hates so much.”

For the Americans, too, a tough road lies ahead. “Washington’s ability to shape developments in regime-held Syria is admittedly weak,” wrote Mona Yacoubian, a senior policy scholar at the United States Institute of Peace. “While Assad remains in power, perhaps the best the United States can hope for is to keep countering the regime’s egregious behavior without further inflaming the conflict.”

But that means reckoning with a regime that is still guilty of slaughtering scores of its own people. On Tuesday, as the battle for Afrin intensified, the regime pummeled the rebel-held Damascus suburb of East Ghouta, killing more than 100 people in what aid agencies described as one of the bloodiest 24 hours of the Syrian war. UNICEF issued a communique with a large blank space, stating that “no words will do justice to the children killed.” It was yet another cry of exasperation and despair in a conflict that is still finding new depths of cruelty to plumb.

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