AMMAN (Reuters) - Syrian rebels have brought at least 2,000 reinforcements through Turkey in the past week to bolster the fight against Kurdish-led militias north of Aleppo, rebel sources said on Thursday.

Turkish forces facilitated the transfer from one front to another over several nights, covertly escorting rebels as they exited Syria’s Idlib governorate, traveled four hours across Turkey, and re-entered Syria to support the embattled rebel stronghold of Azaz, the sources said.

“We have been allowed to move everything from light weapons to heavy equipment, mortars and missiles and our tanks,” Abu Issa, a commander in the Levant Front, the rebel group that runs the border crossing of Bab al-Salama, told Reuters, giving his alias and talking on condition of anonymity.

The reinforcements did not include fighters from the hardline Nusra Front or other jihadist groups, he said.

A Turkish security source confirmed fighters had crossed the border but put the numbers at 400-500, and the British-based Syrian Observatory for Human Rights, which tracks violence across the war torn-country, also said hundreds had crossed.

On Sunday, the Syrian government said Turkish forces were among 100 gunmen who had entered Syria accompanied by 12 pick-up trucks mounted with heavy machine guns, in an ongoing supply operation to insurgents.

The route via Turkey has become the sole supply line for Azaz after the Syrian army closed what for years had been the main route into rebel territory and advanced to within 25 miles of the border for the first time in over two years.

The Syrian army wants to seal it off altogether and reassert full control of Aleppo, Syria’s largest city before the war.

Inside Aleppo city, heavy clashes continued between Arab insurgent groups and Syrian Kurdish fighters in Kurdish-held neighborhoods of Sheikh Maqsoud, the Syrian Observatory said.

Russian bombing has transformed the almost five-year-old civil war in recent weeks, turning the momentum decisively in favor of Moscow’s ally President Bashar al-Assad.

But the rapid advance of U.S.-backed Kurdish fighters has infuriated Ankara and threatened to drive a wedge between NATO allies.

Turkey sees the militia as an extension of the outlawed Kurdistan Workers Party (PKK), which has fought a three-decade insurgency for autonomy in Turkey’s mainly Kurdish southeast.

Determined to prevent the YPG from gaining a foothold on its border, Turkey has shelled its positions in response to what it says is fire coming across the border.

Turkey has also stepped up deliveries of military hardware to the rebels, another rebel source said.

“We are getting fresh supplies of everything from missiles to mortars to armored vehicles. Almost everything is now being delivered to us,” said the rebel source.

Turkish army vehicles were offloading the munitions and equipment onto Syrian rebel armored vehicles and trucks, said the rebel, who was present during a handover of weapons.

New supplies of ground-to-ground missiles with a range of 20 km (12 miles) had been provided to bolster the response to the Russian-backed attack, two rebel commanders said.

Facing one of the biggest defeats of the five-year-long war, rebels have been complaining that foreign states such as Saudi Arabia and Turkey have let them down by not providing them with more powerful weapons, including anti-aircraft missiles.

The rebels and the Turkish government accuse the Kurdish militias of a campaign of ethnic cleansing of Arab-inhabited villages in a bid to carve a fiefdom in Syria’s north.

The YPG has exploited the Russian-backed offensive, seizing ground from other opposition groups. After taking a string of towns, in what the rebels say is an advance coordinated with Russia, the YPG is now seeking to take Marea, the last town before Azaz.