The two rival Palestinian factions have failed to heal their political disputes since Hamas fighters expelled Fatah from Gaza in a short war in 2007
Several groups of militants attacked the Syrian army's artillery battery in the province of Deir al-Zour on Saturday night, killing two Russian military advisers on the spot and wounding another five soldiers.
The injured were immediately taken to a Russian military hospital, but two of them died there, Xinhua news agency reported, citing the Russian Defence Ministry.
The Syrian and Russian troops fought the militants for about one hour and killed 43 militants and destroyed six cross-country vehicles armed with large-calibre weapons, according to the ministry.
Russia has been participating in the fight against the Islamic State (IS) and insurgent groups in Syria since September 2015 at the request of Syrian President Bashar al-Assad.