Syrian troops on Friday retook Deir Ezzor, the last major city where the Islamic State group had a presence, even as Iraqi forces seized a crossing by the jihadists' last urban bastion across the border.
With the new losses, IS has been driven from more than 96 per cent of the large parts of Iraq and Syria it once held, crushing its goal of establishing a "caliphate" in the region.
The simultaneous assaults on Deir Ezzor in eastern Syria and Al-Qaim in western Iraq dealt fresh blows to the IS in its former heartland, leaving Albu Kamal, on the Syrian side of the border, the last town of note under its full control.
The militants are left fighting for a final stretch inside Syria and desert regions along the Iraq-Syria border.
Syrian President Bashar Assad's military on Friday announced the capture of the eastern Syrian city of Deir el-Zour, while Iraqi Prime Minister Haider al-Abadi proclaimed victory in retaking the town of Qaim on the border, the militants' last significant urban area in Iraq.
The jihadist group that once laid claim to a self-styled ''caliphate'' spanning swathes of Syria and Iraq has seen its proto-state crumble in recent months under the pressure of multiple offensives. In October, it lost its one-time de facto Syrian capital Raqa after an assault of more than four months waged by the US-backed Syrian Democratic Forces, a Kurdish-Arab alliance.
On Friday, Syria's army announced that its Russian-backed assault had recaptured all of Deir Ezzor city, in the oil-rich east of the country, while Iraqi forces captured the Husaybah border post on the edge of the town of Al-Qaim.
''The army forces restored security and stability to all of Deir Ezzor city,'' a spokesman for the army command said in a statement broadcast live on state television.
''Deir Ezzor represents the final phase in the complete elimination of Daesh,'' the statement added, using the Arabic acronym for the group. The city ''was the headquarters of the organisation's leadership, and in losing it, they lose their capacity to direct terrorist operations'', the statement added.
State television said engineering units from the army were combing captured neighbourhoods to clear mines and other explosives.
Syrian forces entered Deir Ezzor city in September, breaking an IS siege of nearly three years on government-held parts of the provincial capital.
The battle has been ferocious, with heavy Russian air strikes and Syrian artillery fire leaving much of the city in ruins.
A reporter contributing to AFP inside the city on Thursday saw entire floors of buildings that had crashed onto those beneath, while on others, facades were completely blown away to reveal empty, destroyed interiors.
The Syrian city of Boukamal is the last major urban centre in the hands of IS. The group also is spread along the Syria-Iraq border in villages in the provinces of Hassakeh and Deir el-Zour in eastern Syria.
There also are small IS cells in Iraq's Nineveh, Anbar and Salahudin provinces, where the central government has lacked strong control for years.
Along this thin line on the border of the two countries, the militants still have a presence in a region running west of the Euphrates River toward the Syrian Desert, between Deir el-Zour and Homs provinces. There also is a small IS presence near Damascus.
In a briefing last week, Gen Joseph Dunford, chairman of the US Joint Chiefs of Staff, said small numbers of IS leaders are "attempting to leverage local insurgencies" in Africa and Asia as they lose territory in Iraq and Syria.
The group's militants and local affiliates in Egypt, Libya, the Sahel area of Africa and the Philippines continue to challenge authorities, carrying out regular attacks.