The overnight raids in northern and northeastern Syria killed at least 31 people, said the British-based monitoring group the Syrian Observatory for Human Rights. They were mainly against positions held by Syrian Kurdish forces.

The offensive, codenamed Operation Claw-Sword, comes a week after a blast in central Istanbul killed six people and wounded 81, an attack Turkey has blamed on the Kurdistan Workers' Party (PKK).

The PKK has waged a bloody insurgency there for decades and is designated a terror group by Ankara and its Western allies. But it has denied involvement in the Istanbul explosion.

"Air Operation Claw-Sword was successfully carried out, within the scope of our strategy to eradicate terrorism at its source and eliminate terror attacks against our people and security forces from northern Iraq and Syria," said a defence ministry statement.

The strikes targeted PKK bases in northern Iraq's mountainous regions of Kandil, Asos and Hakurk, and bases of the Kurdish People's Protection Units (YPG), in Ayn al-Arab (called Kobane in Kurdish), Tal Rifaat, Jazira and Derik regions in Syria, the ministry said.

Ankara considers the YPG to be a PKK-affiliated terror group.

In all, 89 targets including shelters, bunkers, caves, tunnels, ammunition depots, so-called headquarters and training camps belonging to the militants "were destroyed", the ministry said, adding "many terrorists were neutralised".

"All our planes safely returned to their bases after the operation," it added.

Defence Minister Hulusi Akar was seen in a video image briefing President Recep Tayyip Erdogan, who gave the order for the latest operation.

Syria's government meanwhile said the raids had killed a number of its soldiers.

Last Sunday's Istanbul bombing was the deadliest in five years, reviving bitter memories of a wave of nationwide attacks between 2015 and 2017.

Those attacks were attributed mostly to Kurdish militants or Islamic State (IS) group jihadists -- but no one has claimed responsibility for the Istanbul attack.

- Rocket attack -

A rocket fired by Kurdish forces in Syria's Tal Rifaat region wounded eight security personnel on the Turkish border, the official Anadolu news agency reported.

Two Turkish soldiers and six police officers were hurt after the rocket fell on the Oncupinar crossing in southern Turkey near the Syrian border, said the agency.

After the Istanbul explosion, Turkish authorities arrested more than a dozen people, including chief suspect Alham Albashir -- a Syrian woman said to have been working for Kurdish militants.

Bulgaria has also detained five people accused of having helped one of the suspects.

"The hour of reckoning has come," the Turkish defence ministry tweeted early Sunday, with a photo of a plane taking off for a night operation.

Nearly 25 air strikes hit the provinces of Raqa, Hassakeh and Aleppo, killing 18 members of the Kurdish-led Syrian Democratic Forces (SDF), 12 members of Syria's military and one journalist, according to the Syrian Observatory for Human Rights.

Kurdish authorities in northeastern Syria gave a toll of 29 dead: 11 civilians, 15 fighters aligned with Syria's military, two silo guards and one Kurdish fighter.

Turkey's military has in the past denied claims its strikes target civilians.

In its first comment on the Turkish strikes, the Syrian defence ministry said "a number of soldiers" had been killed due to "Turkish aggressions in northern Aleppo and Hassakeh provinces at dawn".

- Complex ties with US -

Turkey's latest military push could create problems for its complex relations with its Western allies -- particularly the United States, which has relied mostly on Syrian Kurdish militia forces in its fight against IS jihadists.

Turkey has often accused Washington of supplying Kurdish forces with weapons.

Interior Minister Suleyman Soylu rejected the United States' message of condolences after the Istanbul attack, even though Erdogan accepted them during a meeting on Tuesday with President Joe Biden on the margins of the G20 summit in Indonesia.

Soylu has said Ankara believes the order for the Istanbul attack was given from Kobane, controlled by Syrian Kurdish militia forces, who have also denied any role.

Kobane, a Kurdish-majority town near the Turkish border, was captured by IS in late 2014 before Syrian Kurdish forces drove them out early the following year.

The US-backed SDF said in a statement that the Turkish attacks would "not go unanswered".

Turkey has launched waves of attacks on Syria since 2016 targeting Kurdish militias as well as IS jihadists, and Ankara and forces backed by it have seized territory along the Syrian border.

Since May, Erdogan has been threatening to launch a new operation in northern Syria.

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