Turkey on Wednesday warned that its military would retaliate if any Syrian aircraft violate its airspace amid a third day of air strikes by Syrian forces against rebels who overran a town along the border with Turkey.

An Associated Press video journalist in the Turkish border town of Ceylanpinar witnessed a Syrian air strike in the adjacent Syrian town of Ras al-Ayn, where rebels say they have ousted troops loyal to President Bashar al-Assad.

The Syrian Observatory for Human Rights said Wednesday that warplanes carried out six airstrikes in al-Hasaka, including those at Ras al-Ayn.

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Syrians inspect the damage and looking for victims moments after an airstrike by Syrian warplanes in Ras al-Ayn, Syria on Monday, in this image taken from video obtained from Shaam News Network. (Shaam News Network via AP video)

Regime jet fighters also targeted the rebellious suburbs of Damascus on Wednesday, the Britain-based Observatory said. Heavy clashes between rebel units and Assad's troops were ongoing in the northern city of Aleppo, the Observatory said. The group relies on reports from activists on the ground.

Deadly air strikes began several days ago, and many casualties were rushed into Turkey for treatment. Local officials said as many as 30 people have died since Monday.

Turkey's Anadolu news agency and other Turkish media said several villages west of Ceylanpinar have been evacuated to protect residents from any spillover of fighting between Syrian government forces and rebels. About 1,000 people left Mursitpinar, 180 kilometres from Ceylanpinar, after an appeal from the loudspeakers of local mosques.

Turkey's defence minister, Ismet Yilmaz, indicated that Turkey would use military force in response to any incursions by Syrian aircraft. Last month, Turkish artillery fired on targets in Syria after Syrian shells landed inside Turkey and killed several Turkish civilians in one instance.

"The necessary response will be given to Syrian planes and helicopters that violate our border," Yilmaz said.

Most Syrian border villages in rebel hands: Israel

Meanwhile, Israel weighed in on the growing violence along Syria's borders on Wednesday.  

The Israeli defence minister said "almost all" Syrian villages near the frontier with Israel have fallen into rebel hands.

"Almost all of the villages, from the foot of this ridge to the very top, are already in the hands of the Syrian rebels," Defence Minister Ehud Barak said Wednesday during a tour of the Golan Heights, the strategic plateau that Israel captured from Syria in 1967 and later annexed.

"The Syrian army is displaying ever-diminishing efficiency."

Earlier this week, Israel opened fire across the border after stray Syrian mortar shells flew into the Golan. Israel believes the mortar attack was spillover from the violence in Syria, and not aimed at Israel.

Barak says Israel will remain "vigilant and alert."

Rocket-propelled grenades hit Turkish side of border

Also Wednesday, the AP journalist saw Syrian forces shelling a wooded area near Ras al-Ayn from where rebels had been firing on them. A Turkish official in Ceylanpinar said the sound of shelling was heard throughout the night.

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Turkish soldiers patrol on the Turkish-Syrian border in Ceylanpinar on Tuesday. (Osman Orsal/Reuters)

Two rocket-propelled grenades hit houses on the Turkish side, but there were no injuries, according to the official, who spoke on condition of anonymity because he is barred from speaking to the media on the record.

Ras al-Ayn is located in the northeastern Syrian province of al-Hasaka, an oil-producing region where the population is mostly Kurdish.

The violence in Syria has killed more than 36,000 people since an uprising against Assad's regime began in March 2011. Hundreds of thousands have fled the fighting into neighbouring Turkey, Jordan, Lebanon and Iraq.

Another 11,000 escaped into Turkey last week following the surge of fighting at Ras al-Ayn.