International pressure on Turkish President Recep Tayyip Erdogan increased on Tuesday not to launch a threatened ground offensive against Kurdish fighters in Syria.

Ankara on Sunday launched a series of Operation Claw-Sword airstrikes – which hit dozens of Kurdish militant targets in Iraq and Syria – and announced that its military was once again “at the forefront of terrorists”.

The airstrikes followed a bomb attack in Istanbul that killed six and wounded 81. Ankara blamed the attack on the Kurdistan Workers’ Party (PKK), which is blacklisted as a terrorist group by the European Union and the United States.

The Turkish leader has been threatening a new military operation in northern Syria since May, escalating those threats after this month’s bombing.

“There is no question that this operation will be limited to an airborne operation only,” Erdogan told reporters upon returning home from the opening of the World Cup in Qatar.

The PKK, which has led an insurgency against the Turkish state since 1984, has denied any role in the November 13 bombing, which was the deadliest in five years after a string of attacks in Turkey between 2015 and 2017.

The United States called for a de-escalation late Monday, and Russia said Tuesday it hoped Turkey would exercise “restraint” and refrain from “excessive use of force” in Syria.

“We urge a de-escalation in Syria to protect civilian lives and support the common goal of defeating ISIS,” US State Department spokesman Ned Price said in a statement, citing the fight against the jihadist group Islamic State (IS).

“We understand and respect Turkey’s concerns about its own security… We continue to urge all parties to refrain from any action that could lead to a serious destabilization of the situation,” Kremlin spokesman Dmitry Peskov told reporters.

“We hope to persuade our Turkish colleagues not to use excessive force on Syrian territory,” Alexander Lavrentiev, Russian President Vladimir Putin’s special representative for Syria, told reporters in the Kazakh capital Astana.

“For months, Russia … did everything possible to prevent any large-scale ground operation,” Lavrentiev added.

In return, Turkey asked its allies to stop supporting Kurdish People’s Protection Units (YPG) fighters who supported the US-led campaign against ISIS.

“We tell all our interlocutors, especially the United States, that the PKK is on an equal footing with the YPG, and we urge that all support for the terrorists cease,” Turkey’s Defense Minister Hulusi Akar told lawmakers.

Turkey has launched three offensives in Syria since 2016 to crush Syrian Kurdish fighters whom it accuses of being allied with the PKK.

Erdogan has repeatedly called for a 30-kilometer “security zone” to protect southern Turkey from cross-border attacks from Syrian territory.

At least three people, including a child, were killed in a Turkish border town on Monday by a missile attack launched from Syria.

Anthony Skinner, a Turkey expert and political risk adviser, told AFP that the conditions “are in place” for a particularly robust campaign against Kurdish militants ahead of Turkey’s June presidential and parliamentary elections.

“Erdogan wants to bolster support for his AKP and their (nationalist) MHP allies, so he is playing the nationalist and security card. Hence the noise,” he said.

“Erdogan used the security and stability cards effectively in the run-up to the 2015 general election rerun. But his work is now suspended due to economic and socio-economic pressures.”