(Adds quote, missile range)

By Tom Perry

BEIRUT, Feb 12 (Reuters) - Syrian President Bashar al-Assad's foreign enemies have sent rebels new supplies of ground-to-ground missiles to confront a Russian-backed offensive by the government near Aleppo, stepping up support in response to the attack, two rebel commanders said.

The commanders told Reuters the missiles with a range of 20 km (12 miles) had been provided in "excellent quantities" in response to the attack that has cut rebel supply lines from the Turkish border to opposition-held parts of the city of Aleppo.

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.

"It is excellent additional fire power for us," said one of the commanders, who declined to be identified due to the sensitivity of the matter. The second rebel commander said the missiles were being used to hit army positions beyond the front line. "They give the factions longer reach," he said.

Assad's enemies have been supplying vetted rebel groups with weapons via a Turkey-based operations centre. Some of the vetted groups have received military training overseen by the U.S. Central Intelligence Agency. The Syrian government says it aims to seal the border to cut rebel supply routes from Turkey.

While the Grad missiles fall short of the rebels' demands for anti-aircraft systems, one of the commanders said they had "a significant impact on the army's rear positions". (Reporting by Tom Perry, editing by Ralph Boulton)

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