Welcoming the offensive, the USA -led global military coalition, which has run an air campaign against the Islamic State group in both Syria and Iraq since 2014, said in a statement that approximately 1,500 Islamic State fighters were estimated to remain in the immediate vicinity of al-Qaim.
Syrian troops yesterday retook the last major city where the Islamic State in Iraq and Syria (ISIS) group had a presence in the country as Iraqi forces punched into the Islamists' last urban bastion across the border.
The US-led coalition congratulated the Iraqi government and the Iraqi Security Forces (ISF) in a statement.
Home to around 150,000 people, it is one of the last remaining territories in the country still held by ISIS militants after rampaging across Iraq and Syria in 2014.
Meanwhile the Syrian government, which is backed by Russian Federation has regained complete control of the eastern city of Deir al-Zor on Friday, representing a huge blow to the jihadists as their last stronghold in Syria crumbles.
Syrian government forces and their pro-government allies first broke the militant group's siege of their part of the city in September and have been advancing against ISIS positions since then. The Iraqis, with the support of the global coalition, have now liberated almost all of the territory once held by ISIS in Iraq, they said.
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He estimated there were 1,500-2,500 fighters left in al-Qaim and 2,000-3,000 in Albu Kamal.
A military source said: "The armed forces, in cooperation with allied forces, liberated the city of Deir al-Zor completely from the clutches of the Daesh terrorist organisation".
Driven this year from its two de facto capitals - Iraq's Mosul and Syria's Raqqa - both the Iraqi and Syrian governments and their global backers say they worry that ISIS will still be able to mount guerilla attacks once they no longer have territory to defend.
"Several terrorists were killed and a number of booby-trapped vehicles destroyed during the operation", he said, adding that most remaining ISIS militants had since fled the area towards Al-Qaim.
The UN said the executed civilians were among at least 2,521 who were killed during the battle for the city, mostly from ISIS attacks, including indiscriminate shelling and the use of improvised bombs and explosive-laden drones.