BEIRUT • The Islamic State in Iraq and Syria (ISIS) group recaptured Albu Kamal in eastern Syria after a fierce fightback to save the last urban bastion of its collapsing "caliphate".

The rebound last Saturday came as the United States and Russia issued a surprise joint presidential statement saying there was "no military solution" to Syria's grinding six-year war.

The two countries have long backed opposite sides in Syria, but the Kremlin on Saturday said US President Donald Trump and his Russian counterpart Vladimir Putin made progress during a brief meeting on the sidelines of a regional summit in Vietnam.

Both leaders also "confirmed their determination to defeat ISIS".

The militant group overran swathes of territory in Syria and Iraq in 2014, but its self-styled caliphate has since been whittled down to a pocket of land along the border between the two countries.

ISIS is putting up a fierce defence there, particularly for the vital border town of Albu Kamal, said the Syrian Observatory for Human Rights monitoring group.

Syrian regime forces and allied militia from Lebanon, Iraq and Iran overran Albu Kamal last Thursday, but lost the town again just two days later after a string of ISIS counter-attacks and ambushes.

Albu Kamal is the last significant Syrian town ISIS controls. Losing it would cap the group's reversion to an underground guerilla organisation with no urban base.

"ISIS fully recaptured Albu Kamal, and regime forces and allied militia are now between 1km and 2km from the city limits," said Mr Rami Abdel Rahman, head of the Britain-based Observatory.

The monitoring group 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.

Albu Kamal is the last significant Syrian town ISIS controls. Losing it would cap the group's reversion to an underground guerilla organisation with no urban base.

On Saturday, Jordan announced it had agreed with the US and Russia to formally establish a "de-escalation" zone in southern Syria to build on a ceasefire already in place there.

Multiple rounds of peace talks hosted by the United Nations in Geneva have failed to resolve Syria's entrenched conflict.

The joint US-Russia statement urged Syria's warring sides to take part in a new round of talks later this month in Switzerland.

AGENCE FRANCE-PRESSE