Since then, Erdogan’s government has orchestrated a steady stream of leaks to the media with grisly details of the murder, piling pressure on Salman, who has denied involvement despite the alleged role of senior Saudi intelligence officials in the slaying. The reports of Khashoggi’s gruesome murder have depicted the Saudi government as ruthless in its crackdown on dissidents and tested the kingdom’s relations with the West.

Turkey’s active role on Syria appears to be part of Erdogan’s wider strategy to reassert Turkish influence in the region. Nowhere is this more apparent than in the Turkish president’s high-stakes standoff with Saudi Arabia’s crown prince, Mohammed bin Salman, over the case of murdered journalist Jamal Khashoggi, a Washington Post columnist who was killed at the Saudi Consulate in Istanbul Oct. 2.

The attack also followed a summit on Syria in Istanbul, hosted by Erdogan and attended by the leaders of Germany, France and Russia on Saturday. They called for a new Syrian constitution to be drafted before the end of this year, “paving the way for free and fair elections,” according to a joint statement.

The shelling of People’s Protection Units (YPG) positions on the Euphrates’ eastern shore on Sunday came just two days after President Recep Tayyip Erdogan gave his “final warning” to Syrian Kurdish fighters to retreat and accused the United States of dragging its feet in an agreement to remove the group from Turkey’s border.

Turkey’s attack on Kurdish militants east of the Euphrates River in northern Syria for the first time escalates its fight against the US-allied group and raises the risk of a confrontation with American forces fighting alongside the rebels.

Ties between Ankara and Riyadh were strained before Khashoggi’s death over divergent views on Syria, Iran and Israel, and some observers describe Turkey’s pressure campaign on the Saudis as a battle between Erdogan’s nominally democratic version of political Islam and the absolute theocracy of Saudi Arabia, one of the world’s biggest oil producers and the dominant force in the region.

For his part, Erdogan has worked closely with Russia, despite supporting opposite sides of the Syrian conflict, as Turkey’s relationship with the United States has soured in recent years over delays in arm sales, the jailing of an American pastor in Turkey, the US collaboration with the YPG and Erdogan’s perceived tilt away from the trans-Atlantic alliance.

Last month, Erdogan brokered a cease-fire in the Syrian town of Idlib, controlled by the rebels Turkey backs, with Vladimir Putin, Syrian President Bashar al-Assad’s greatest defender, forestalling an imminent bombardment of the province where more than 3 million civilians live. At the Istanbul summit, French President Emmanuel Macron told reporters: “Russia and Turkey have negotiated an agreement that must be strictly implemented. Assurances were made on this point.”

Macron said, “We are counting on Russia to exert a very clear pressure on the [Syrian] regime, which very clearly owes it its survival.”

In June, NATO allies Turkey and the United States agreed to the withdrawal of YPG forces from the Syrian town of Manbij, which the Kurdish fighters helped clear of Islamic State (IS) militants in 2016. But Erdogan has repeatedly accused Washington of delays in the deal.

Turkey views the YPG as a terrorist organization because of its close links with the Kurdistan Workers Party (PKK), an armed group that has waged a three-decade campaign of violence for greater autonomy for Turkey’s 16 million Kurds. Its presence on Turkey’s long border with Syria poses a national security threat, Erdogan says, and in January, the Turkish army and the fighters it backs took the Syrian province of Afrin from the YPG after taking another swath of Syrian territory to stymie Kurdish advances in 2016. Turkey now controls some 4,000 square kilometers of Syria.

Turkey fired howitzers against YPG targets east of Kobani in what appeared to be a limited offensive. Kurdish militants said one of their fighters was killed in Sunday’s assault and accused Turkey of “indirectly helping IS.” It vowed “no attack against the northern Syrian territory will be left unanswered,” according to a statement on a YPG website.

“The Turkish government uses its military to great diplomatic effect with the United States,” Aaron Stein, a senior fellow at the Atlantic Council, told Al-Monitor. “What Ankara is trying to do is to signal its continued displeasure with the status quo in Syria and to force the United States to make concessions. This was the model that led to the Manbij road map. Ankara would like to see this model replicated east of the river, so that it essentially will get a ribbon of controlled territory along the border to push the YPG deeper into Syria and off the border.”

But if Turkish forces delve further east into Syria, they could face off with American troops. The United States has armed and trained the YPG in its fight against IS in Syria since 2014 and keeps some 2,000 of its special forces in areas controlled by the Kurds.

Stein said the delays in the agreement on Manbij have been due to negotiations on how to implement it, including the rules of engagement for patrols of the town and the locations of the patrols.

“Ankara wants to get into the city. The US wants the patrols limited to around the forward line of contact and in designated areas. There is a lot that needs to be settled, even though I expect the patrol will begin in November,” Stein said, adding he believes the two sides have agreed that the US military will be in command.

Meanwhile, the investigation into Khashoggi’s death continues in Istanbul, with Turkey continuing to demand greater cooperation from Saudi authorities. Turkish Foreign Minister Mevlut Cavusoglu warned on Monday that Saudi Arabia must not stall the investigation.

A top Saudi prosecutor met with Turkish counterparts for the first time in Istanbul on Monday. Over the weekend, Saudi authorities rejected Erdogan’s demand that Riyadh extradite to Turkey the 18 citizens it arrested for their alleged involvement in his killing.