The Turkish army blamed the Syrian regime for an air strike Thursday in northern Syria that killed three soldiers -- the first time it has accused Damascus of killing its troops since launching its three-month military incursion.

The incident came on the first anniversary of the shooting down of a Russian military jet over the Syrian border by the Turkish air force.

That led to a seven-month crisis in relations between Turkey and Russia, an ally of Syrian President Bashar al-Assad that has provided military support to Damascus.

The army said the strike took place at 3:30 am (0030 GMT). It did not indicate the location, although local media said it took place in the Al Bab region.

"In the air strike assessed to have been by Syrian regime forces, three of our heroic soldiers were killed and 10 soldiers wounded, one seriously," the armed forces said in an online statement.

Turkish media reported earlier that the attack was by Islamic State (IS) jihadists.

Adding to the confusion, the Britain-based Syrian Observatory for Human Rights said it was an "attack by IS" on its website.

But Turkish Prime Minister Binali Yildirim insisted at a news conference that the army's statement was "still valid".

He said it was evident that "some are not happy with Turkey's fight against Daesh (IS)", without indicating who this might be.

Yildirim vowed that the attacks would be "given a response" and would not diminish the military's determination to remove "terrorists" in the region.

But Turkey's main opposition Republican People's Party (CHP) chief Kemal Kilicdaroglu warned that the incident could drag the country "into a very dangerous process" and called for the government to act with "common sense".

The prime minister's office slapped a broadcasting ban on coverage of the strike an hour after the military's statement, Turkey's broadcast watchdog said on its website.

The injured soldiers were taken to hospitals in the southeastern cities of Kilis and Gaziantep close to the Syrian border, the official news agency Anadolu said.

Anadolu said another seven Turkish soldiers were lightly injured in a second attack blamed on IS on Thursday evening in the same region and taken to Kilis for medical treatment.

- 'First Al Bab then Manbij' -

The Turkish military launched an operation -- dubbed "Euphrates Shield" -- with tanks and air power in August to support Syrian opposition fighters seeking to retake territory from IS in northern Syria.

Ankara-backed rebels comprise several brigades rather than one organised force, according to experts.

Hundreds of Turkish soldiers are taking part in the operation, which Erdogan said this week was pushing forward with its aim of taking Al Bab from IS.

The operation has also targeted Syrian Kurdish militia, whom Ankara views as linked to its outlawed Kurdistan Workers' Party (PKK), which has staged an insurgency in Turkey since 1984.

The PKK is proscribed as a terror group by the US and EU but not by the United Nations.

"After that (Al Bab), we will go towards Manbij" to remove elements from the Syrian Kurdish Democratic Union Party (PYD) and People's Protection Forces (YPG) militia, Erdogan said.

Kurdish-led forces recaptured Manbij from IS in August but Ankara has called for them to leave what Turkey emphasises is an Arab majority town.

Since the offensive began, the rebels captured the IS stronghold of Jarabulus, cleared IS from Al Rai and retook the symbolically important town of Dabiq without much resistance.

The latest deaths raise to at least 15 the number of Turkish soldiers killed since Turkey began its operation in northern Syria.

Most were killed by IS but one soldier died in an attack blamed on the YPG militia.

- Assad presses Aleppo offensive -

Amid a rapprochement with Russia, Turkey has largely been tight-lipped as Assad's Moscow-backed forces press an offensive to recapture the whole city of Aleppo, which is divided between the government and rebels.

The government last week resumed its drive to retake the city's east, where more than 250,000 civilians have been under siege for months, with dwindling food and fuel supplies.

On Wednesday, the Syrian Observatory for Human Rights said dozens of civilians had tried to flee but were forced back by gunfire.

Save the Children called for an internationally-monitored ceasefire to allow aid into east Aleppo and the evacuation of sick and wounded civilians.