While Syria apologised for the attack, which claimed the lives of three children, Turkey’s parliament authorised the government to use force against the Assad regime whenever it deemed necessary.
The country’s prime minister, Recep Tayyip Erdogan, warned that Turkey’s determination to defend its citizens, and its borders, “should not be tested”. But world leaders led by Ban Ki-moon, the United Nations secretary-general, and William Hague, the Foreign Secretary, urged Mr Erdogan to avoid any further escalation of the crisis.
Mr Hague spoke to his Turkish opposite number, Ahmet Davutoglu, by telephone to say that while Ankara had the unequivocal backing of the international community it should “use it carefully”.
“We express our strong solidarity with Turkey but we don’t want to see a continuing escalation of this incident,” he told reporters later, while on a visit to Hungary. Germany, the European Union, and China all appealed for restraint.
The US also indicated that it thought the Turkish response had gone far enough.
At a news conference last night, Mr Erdogan attempted to reassure Western powers by insisting his country was not interested in starting a war.
However, he added: “The Turkish Republic is a state capable of defending its citizens and borders. Nobody should try and test our determination on this subject.”
Since the start of the Syrian uprising last year, Turkey has abandoned its previous growing friendship with the Assad regime and become one of its leading critics. In recent months it has called for an internationally backed safe or buffer zone for refugees in the north of the country.
The latest crisis began on Wednesday when four Syrian mortar shells aimed at the Tal Abyad border post on its side of the border, landed instead on the Turkish side in the town of Akcakale.
One injured a policeman, a second hit a grain mill and the third hit the courtyard of a house, killing Zeliha Timucin, her sister-in-law and her three daughters.
The town is part Arab, and many residents have relatives living in Syria. While much of Turkey is uneasy about the prospect of being dragged into war, Mr Erdogan’s hard-line stance has strong support in the town.
“We don’t want to be in a war, but if they push us to war, we will have war,” said Mustafa Taka, 58, a civil servant, one of several men standing in silent demonstration outside the town hall yesterday.
The houses alongside the frontier have increasingly emptied as the fighting has crept closer in recent weeks. As in other parts of the Syrian border, both with Turkey and with Lebanon, the regime has shown little compunction in using artillery fire up to the frontier lines and even beyond in its attempts to deter rebels.
Syrian troops previously killed two refugees when shooting over the border towards a refugee camp further to the west. One resident said up to 70 per cent of the town had taken refuge in the nearby city of Sanliurfa. “We don’t feel safe,” the resident said. “We are worried.”
The Turkish military moved a string of armoured vehicles up to the border immediately after the Tal Abyad crossing fell, residents said, their gun-turrets pointed menacingly at the Syrians. Another armoured vehicle moved down Ceylanpinar Street, where three of the four Syrian shells fell.
According to the Syrian Observatory for Human Rights, the Turkish shelling killed a number of Syrian soldiers at the military base about 10 miles from Tal Abyad from which the original mortar attack originated. There was no confirmation from the Syrian authorities.
Syria was forced partly by diplomatic pressure from Russia, its main backer on the UN security council, to issue an apology.
But by the time the apology was received, the Turkish government had already pressed ahead with a vote authorising it to use force in Syria. The mandate lasts for a year.