Turkish armed forces have launched artillery attacks on a Syrian area near its border in response to a mortar attack which killed five members of the same family in southeastern Turkey.
Turkish state media has said that Turkey resumed cross-border artillery strikes at Syrian targets on Thursday.
There are unconfirmed reports that several Syrian troops were killed as a result of overnight Turkish shelling across the border in Tal al-Abyad.
The government in Ankara is expected to ask the parliament on Thursday to authorise cross-border military operations in Syria, according to Turkish media reports.
In a statement on Wednesday, Recep Tayyip Erdogan, Turkey's prime minister, said the attacks, carried out following radar tracking, were within the rules of engagement.
Separately, Bulent Arinc, the deputy prime minister, said: "There has been an attack on Turkey's mainland and its citizens lost their lives. There is definitely a response to it in international law ... We are not blinded by rage, but we will protect our rights to the end in the face of such an attack on our soil that killed our people."
Al Jazeera's Andrew Simmons, reporting from Antakya on the Turkish-Syrian border, said Arinc's mention of "certain responsibilities" contained within NATO treaty articles, could mean that Turkey responded without consulting international bodies first.
Turkey has also asked the United Nations Security Council to take "necessary action" to stop Syrian aggression, calling the mortar attack "a flagrant violation of international law".
The Syrian Observatory for Human Rights (SOHR) said: "Several shells from the Turkish side of the border fell on Syrian military positions near the village of Tal al-Abyad".
Western officials, from Anders Fogh Rasmussen, the NATO secretary-general, to Hillary Clinton, the US secretary of state, quickly condemned the initial attack from the Syrian side of the border, which struck a house in the border town of Akcakale.
Omran Zoabi, Syrian information minister, said Damascus was looking into the origin of the deadly cross-border shelling.
In a statement reported by state television, Zoabi said: "Syria offers its sincere condolences to the families of the victims and to our friends the Turkish people".
Though this, the mortar attack, marks the third instance of Syrian gunfire or artillery reaching Turkish territory, it is the "first time Turkey has actively become involved" in the situation, our correspondent said.
Calling it a "very serious escalation", he said the last time there was such tension between the neighbouring countries was when a Turkish war plane was downed in June. However, Turkey did not retaliate in that instance.