Turkey will strike Syrian government forces "anywhere" if one more Turkish soldier is hurt and could use airpower if need be, President Recep Tayyip Erdogan has said.
Addressing the country's parliament in Ankara on Wednesday, Erdogan said Turkey is determined to push Syrian government forces beyond Turkish observation posts in the northwestern Idlib region by the end of February.
"We will do this by any means necessary, by air or ground," he said.
Turkey has set up 12 observation posts in the last rebel-held stronghold in Syria as part of a 2018 deal with Russia, which backs Syrian President Bashar al-Assad.
This month it has poured thousands of troops and convoys of military vehicles across the border into Idlib, including tanks, armoured personnel carriers and radar equipment to bolster its existing military positions.
Syrian government attacks have killed 13 Turkish military personnel in Idlib this month, prompting a deadly response from Ankara amid concerns over an escalation of violence in the country's nearly nine-year war.
On Tuesday, Erdogan said the Syrian government will pay a "very heavy price" for attacking Turkish troops in Idlib.
Ankara has said it retaliated for both attacks, destroying scores of Syrian targets.
Turkish-backed rebels have mobilised to push Syrian government forces out of Idlib, Erdogan said, adding they must remain disciplined.
"We have given the message that we will act without compromise to those from the opposition groups who act in an undisciplined way and give the regime an excuse to attack," he said.
With backing from Russia, Syrian troops have been on the offensive for weeks in Idlib province and parts of nearby Aleppo, triggering a humanitarian crisis with some 700,000 people fleeing their homes. Hundreds of civilians have also been killed, according to the United Nations.
Much of the fighting in the past week has focused on the M5 highway, linking the former economic hub of Aleppo to the capital Damascus to the south.
Both Ankara and Moscow agreed in September 2018 to turn Idlib into a so-called de-escalation zone where acts of aggression are expressly prohibited.
The Syrian government and its allies, however, have consistently broken the terms of the ceasefire - including a fresh ceasefire that started on January 12 - launching frequent deadly attacks inside the zone.
The Turkish military casualties have strained ties between Ankara and Moscow, which back opposing sides in the conflict but have reached a number of agreements in an attempt to find a resolution.
On Wednesday, the Kremlin said Russian President Vladimir Putin spoke to Erdogan about defusing the situation in Idlib and said the sides should defer to existing Russian-Turkish agreements - which deal with the implementation of the de-escalation zones - and should be implemented in full.
"The importance was noted of the full implementation of existing Russian-Turkish agreements," the Kremlin said in a statement after the Putin-Erdogan phone call.
However, the Kremlin accused Turkey of flouting agreements it had made with Russia to neutralise armed fighters in Idlib and said attacks on Syrian and Russian forces in the region were continuing.
Spokesman Dmitry Peskov said Russia considered these attacks as unacceptable and in contravention of the agreements made.
"In particular, according to this document (agreement), the Turkish side undertook to ensure that terrorist groups in Idlib were neutralised," he said.
"We continue to note with regret that these groups are carrying out strikes from Idlib on Syrian foces and also taking aggressive action against our military facilities," Peskov told reporters on a conference call.
"This is unacceptable and runs contrary to the Sochi agreements."
Erdogan said Russian and Syrian government attacks have targeted not terrorists but civilians.
"Russian forces and Iran backed militias are constantly attacking the civilian people, carrying out massacres, spilling blood," he said.
Reporting from the Syrian town of Bab al-Hawa, Al Jazeera's Sinem Koseoglu said the Syrian government does not recognise the de-escalation zone criteria.
"Experts told me that after the last meeting in Moscow between the intelligence chiefs of Turkey and Syria, everybody unwillingly accepted that and knew that the Syrian government would advance towards the M5 highway - which is vital for both the Syrian opposition and the government," she said.
"But it wasn't expected that the Syrian government would take over Saraqeb, and when they tried to move towards the town, that was when the Turkish military established some extra observation posts in order to protect its own military posts and civilians."
The M5 links the capital Damascus to the second city of Aleppo through the big hubs of Homs and Hama and has been a key target for the government as it seeks to restore territorial control and rekindle a moribund economy.
Koseoglu said the situation on the ground is "very tense" because both the Syrian government and Turkish side seem "not to be compromising" in their actions.
"Right now Turkey continues with its reinforcements while the Syrian government is enhancing its positions and clashes are under way," she said.
US troops open fire on locals in Qamishli
In a separate development, Syria's state news agency SANA reported one Syrian was killed and another wounded when U.S. forces opened fire on people after their vehicles were stopped at a checkpoint, east of Qamishli.
It was not immediately clear whether the person killed was a civilian or part of the Syrian government forces.
SANA said the shooting was followed by an air strike on a village in rural Qamishli, near the border with Turkey. Turkey's state-owned Anadolu agency said two air attacks took place.
According to the state news agency, locals had gathered at the army checkpoint in the village of Khirbet Ammu, east of Qamishli, pelting the US convoy with stones and taking down a US flag from one vehicle. At that point, US troops fired with live ammunition and smoke bombs at the residents, the report said.
State-run Al-Ikhbariya TV aired a cellphone video showing an armored vehicle flying a US flag standing on a rural road while a car appeared to be blocking its way.
Locals are seen walking past the US armored vehicle, with at least two soldiers inside, one of whom steps down as civilians approach. One civilian is seen tearing a US flag as he approaches the soldier.
The US-led coalition said that US troops near Syria's Qamishli returned fire after "unknown undividuals" opened fire at their patrol.