ISIS makes claims of inflicting more casualties while changing tactics amidst heavy bombing

After the initial shock of intensive Russian air strikes, Syrian rebels on the receiving end of a major offensive say better organization and new tactics have helped them to stem losses and fight back.

A month of Russian air strikes in support of government offensives have cost the rebels in lives and supplies: commanders have been killed, bases bombed, and weapons depleted.

Supported by Iran's Revolutionary Guard Corps and Lebanon's Hezbollah, this is the first multi-pronged attack of its kind in nearly five years of war that have diminished President Bashar al-Assad's control to a quarter or less of Syria.

But while it may be too early to say how this new phase of the war will play out, analysts say modest government gains so far do not appear to match the scale of its assault.

Rebels have even regained some positions, and fighters on the government's side are meanwhile being killed in large numbers, according to the Syrian Observatory for Human Rights, which tracks the war.

Rebels interviewed by Reuters say they are learning to live with Russian air strikes. They are working more closely together and using different tactics to fight back. Knowledge of the terrain is cited as a crucial advantage.

"It's a battle of ambushes, of surprise attacks," said a former army lieutenant-colonel who leads the Jabhat Sham group, a recipient of military support from Assad's foreign enemies that fights under the banner of the Free Syrian Army (FSA).