Video: Turkey blocks Twitter
They have been fighting over what had been the last remaining border crossing with Turkey still in the Syrian Government's hands.
The Turkish military said it issued four warnings to the two jets as they approached its airspace, but one crossed into its territory at Yayladagi, east of the border crossing, near the village of Kasab in Syria's far northwest.
The crossing allows rebels direct access to the heartlands in Latakia province of President Bashar al-Assad's Alawite sect. It was seized by rebels on Friday, but the regime reinforced its troops over the weekend and was continuing to besiege it.
One of the two jets was seen to turn back but the Turkish military said that the other trespassed more than a kilometre inside Turkish airspace.
The order was then given to shoot it down. Shortly afterwards a dramatic vertical trail of smoke marked the spot where the plane had apparently nosedived from the sky.
The pilot was said to have ejected into Syrian territory and, according to one report, made it safely to a regime checkpoint, while the plane crashed 1300m inside Syria, not far from Kasab.
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Erdogan's announcement of the downing of the Syrian jet was made at an election rally. It followed a week in which he has come under intense scrutiny for his attempts to ban Twitter in Turkey and accusations of dictatorial behaviour in advance of municipal ballots.
One of the two main opposition parties, the CHP, described the incident as "a dictator's adventure marching us to war".
But Erdogan won the immediate backing of his own party, which has not always been the case in recent days.
President Abdullah Gul, who attacked Erdogan's ban on Twitter last week, congratulated the Turkish chief of staff, General Necdet Ozel.
"You have shown resolution and determination with regards to the protection of Turkey's borders," he said.
Cemil Cicek, the Speaker of the Turkish Parliament, said his country had acted within international law.
It is not the first aerial clash since the start of the civil war in Syria, where Turkey has taken the side of the rebels and allowed its territory to be used to funnel in money, men and supplies. In June 2012, Syrian forces shot down a Turkish jet off the coast, saying it had encroached on its airspace.
Last September, a Syrian helicopter was shot down over the northern border.
There have also been exchanges of artillery fire, provoking the most serious Nato involvement, with Germany, Holland and the United States all sending Patriot anti-missile batteries to the Turkish border.
Turkey remains a member of Nato, despite the anti-Western rhetoric often deployed recently by Erdogan.
An attack on its territory could theoretically trigger Nato intervention in the war under the "mutual defence" provisions of Article 5 of the North Atlantic Treaty.
The angry Syrian reaction to the incident made no mention of a military response.
"This escalation came in the framework of the aggressive policies of Erdogan's Government and its openly provided support to the armed terrorist groups," the regime said. TelegraphGroup Ltd
