Hezbollah's leader Hassan Nasrallah says the Lebanese militant group will send more fighters to Syria's Aleppo province, where pro-government forces are battling Syrian rebels on several fronts.

Nasrallah gave a speech on Friday, calling the fight for Syria's largest city and its province the "great" battle of the Syria war.

He said Hezbollah "will increase our presence in Aleppo," and added that "there can be no retreat, and no doubt."

Hezbollah, which is also part of the Lebanese government, has sent thousands of fighters to support Syrian President Bashar Assad's forces in the civil war next door. The conflict is now in its sixth-year. Over 1,000 of Hezbollah's fighters have been killed in battle.

Nasrallah admitted to losing 26 fighters in the Aleppo region in June alone.