Syrian rebels fired machineguns mounted on the back of pick-up trucks into the air as jets flown by forces loyal to President Assad resumed bombing raids on the border town of Ras al-Ain.
The planes dropped three bombs, a Reuters witness said, before returning for a second strike on another part of the town, which is metres from Turkey.
The second day of bombings caused residents on the Turkish side to scurry for cover.
Syrian fighter jets flown by forces loyal to President Assad have this morning reportedly resumed bombing of the rebel-held town of Ras al-Ain on the edge of the Turkish border.
The attack, seen by a Reuters witness, sent thick plumes of smoke into the air for the second day.
Yesterday's attack saw scores of Syrians flee over the border, days after rebels gained control of the town.
At least a dozen people died in today's air strikes by Syrian warplanes along the Turkish frontier, according to opposition activists.
The pro-opposition Syrian Observatory for Human Rights put the death toll from the bombing of the rebel-held town of Ras al-Ain at 12, including seven Islamist militant fighters.
Syrian grassroots opposition group, the Local Coordination Committees, said 16 people had died.
NATO will defend alliance member Turkey, which struck back after mortar rounds fired from Syria landed inside its border, the alliance's Secretary General Anders Fogh Rasmussen has said.
– NATO Secretary General Anders Fogh Rasmussen
NATO as an organisation will do what it takes to protect and defend Turkey, our ally. We have more plans in place to make sure that we can protect and defend Turkey and hopefully that way also deter so that attacks on Turkey will not take place.
Speaking at a meeting in Prague, he also welcomed a weekend agreement by Syrian opposition groups to put aside differences and form a new coalition.
Turkish police fired tear gas and water cannon to keep people on the Turkish side away from the border fence while a Syrian warplane - supported by helicopters - attacked just over the border.
In neighbouring Ceylanpinar, anxious residents crowded outside a teahouse to watch the bombing.
One unnamed Turk said:
I thought the Turkish government said it wouldn't allow these helicopters to come so close to the border. Look, they're coming inside our border.
There remains no word on casualties after a Syrian warplane bombed the rebel-held town of Ras al-Ain, barely metres from the Turkish border.
The attack sent scores of Syrian civilians rushing for safety in the neighbouring country.
Helicopters also strafed targets near the town, which fell to rebels on Thursday.
A Reuters reporter in Ceylanpinar - the Turkish settlement that borders Ras al-Ain - said the warplane flew right along the border and appeared at one point to have entered Turkish airspace.
Scores of Syrians have scrambled to cross the border fence into Turkey after the town of Ras al-Ain was bombed by a fighter jet flown by forces loyal to President Assad, a Reuters witness has said.
The bombing sent up huge plumes of black smoke as Assad forces tried to wrest control of the area back from rebels, the witness said.
A Syrian fighter jet has bombed the town of Ras al-Ain near the border with Turkey, a Reuters witness has said.
Forces loyal to Syrian President Assad bombarded Ras al-Ain over the weekend.
The town fell to the Free Syrian Army on Thursday, sending 9,000 fleeing the area within a day.