Ankara launched a series of air strikes in Operation Claw-Sword on Sunday -- hitting dozens of Kurdish targets across Iraq and Syria -- and announcing that its military was once again "on the top of the terrorists".

The air raids followed a bombing in Istanbul that killed six people and wounded 81. Ankara blamed the attack on the Kurdistan Workers' Party (PKK), which is blacklisted as a terror group by the European Union and the United States.

The Turkish leader has threatened a new military operation into northern Syria since May and upped those threats in the wake of this month's attack.

"We have been on top of terrorists for a few days with our planes, cannons and drones," Erdogan told a ceremony in the Black Sea province of Artvin.

"God willing, we will root out all of them soon with our tanks, artillery and soldiers."

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

-'De-escalation'-

The United States late Monday urged de-escalation and Russia said Tuesday it hoped Turkey would exercise "restraint" and refrain from "excessive use of force" in Syria.

"We understand and respect Turkey's concerns regarding its own security... We still call on all parties to refrain from steps that could lead to seriously destabilising the situation," Kremlin spokesman Dmitry Peskov told reporters.

Erdogan said Tuesday his government knew "who protects, arms and encourages those terrorists", in a veiled reference to Washington, which relied heavily on Syrian Kurdish forces in the fight against the Islamic State group.

He said Turkey was patient enough, "not because it was desperate", but because it was loyal to diplomacy.

"The road has come to an end for those who think they can keep Turkey waiting by playing with letters and changing the name of the terrorist organisation," said Erdogan.

Turkey has launched three offensives into Syria since 2016 aimed at crushing Syrian Kurdish fighters, whom it charges are allied to the PKK.

A base in northeastern Syria used jointly by Kurdish forces and the US-led coalition was hit in a Turkish drone strike Tuesday, the Kurds and a war monitor said.

"A joint base north of Hasakeh used for planning and executing joint operations against the Islamic State group has been hit by a Turkish drone," a spokesman for the Kurdish-led Syrian Democratic Forces, Farhad Shami, told AFP, adding that two SDF fighters had been killed.

A Britain-based monitoring group, the Syrian Observatory for Human Rights, confirmed the joint base had come under attack but was not immediately in a position to say whether coalition forces had been present at the time.

There was no immediate comment from the US-led coalition.

-'Robust campaign'-

Erdogan has repeatedly called for a 30-kilometre (19-mile) "safe zone" to protect Turkey against cross-border attacks from Syrian territory.

At least three people, including a child, were killed in a Turkish border town Monday by a rocket strike fired from Syria.

Anthony Skinner, a Turkey expert and a political risk consultant, told AFP that conditions "are in place for a particularly robust campaign" against Kurdish fighters ahead of Turkish presidential and parliamentary elections in June.

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

"Erdogan effectively used the security and stability cards in the run up to the rerun of the general election in 2015. But his work is cut out now because of economic and socioeconomic pressures."