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The Islamic State (ISIS) group on Saturday recaptured Albu Kamal in eastern Syria from the Syrian army, AFP reported.

The jihadist group overran swathes of territory in Syria and Iraq in 2014 and declared a "caliphate" in those areas, but the “caliphate” has since been whittled down to a pocket of land along the border between the two countries.

Earlier this week, Syrian troops and allied militiamen entered the jihadist-held Albu Kamal. A day later, pro-regime media sources in Syria declared the town free of Islamist terrorists.

However, the pro-regime forces lost the town again just two days later after a string of ISIS counter-attacks and ambushes.

"ISIS fully recaptured Albu Kamal, and regime forces and allied militia are now between one to two kilometers from the city limits," Rami Abdel Rahman, head of the Britain-based Observatory, said on Saturday, according to AFP.

The Observatory also reported 26 civilians killed, including nine children, since Friday night in artillery fire by regime forces and Russian air strikes that hit villages and camps for those displaced by the fighting in Albu Kamal.

Albu Kamal remains the last significant Syrian town controlled by ISIS, which recently suffered a series of stunningly quick defeats, including the loss of their de facto capital Raqqa further north.

ISIS rose to prominence in the chaos of Syria's conflict, which broke out in 2011 with protests against President Bashar Al-Assad.

It has since evolved into a complex war that has killed more than 330,000 people, forced millions more to flee, and left much of the country in ruins.

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