Tehran says several of its soldiers have been killed in fighting near Aleppo, in what could be one of Iran’s biggest losses in Syria since deploying forces to support Syrian President Bashar al-Assad.

The Fars news agency on May 7 quoted a Revolutionary Guards official as saying that 13 military advisers had been killed and 21 wounded in the clashes with Islamist insurgents on May 6 in Khan Tuman, some 15 kilometers southwest of Aleppo.

According to Reuters, dozens of people were killed in the battle.

Reports said the attack on Khan Tuman was launched by an alliance of Islamist insurgents known as Jaish al-Fatah, including the Al-Qaeda-linked Nusra Front.

Jaish al-Fatah and its affiliates have published on videos and photos on social media of what appear to be the bodies of Iranians or other Shi'ite militias who were killed in Khan Tuman.

Earlier this week, the United States and Russia brokered a cease-fire in the city of Aleppo itself. But fighting in the countryside to the south of the city has escalated in recent days.

In related news, a senior Iranian official has met with Assad and vowed continued support for his government in the country's five-year-old civil war.

Ali Akbar Velayati, an adviser to Iranian Supreme Leader Ayatollah Ali Khamenei, met with Assad in Damascus on May 7.

Syria's state news agency SANA quoted Velayati as saying that Tehran will always stand by Syria because it "knows that terrorism does not target Syria but the whole people of the region."

Velayati's comments came as Russia's Defense Ministry announced that a cease-fire in the northern Syrian city of Aleppo has been extended by three days starting on May 7.

The Russian Defense Ministry statement early on May 7 said the extension was made at Moscow's initiative and would also apply to the Latakia region.

With reporting by Reuters and AP