So-called Islamic State (IS) has lost more than a quarter of the territory it once controlled, new data shows.
Security and defence analysts IHS say the group's control has shrunk by 28% since its height in January 2015.
In the first nine months of this year, IS' territory fell from 78,000 sq km (30,115 sq miles) to 65,500 sq km - an area equivalent to the size of Sri Lanka - IHS analysts said.
However, IS losses have slowed in the three months to October.
IS has lost just 2,800 sq km (1,080 sq miles) since July.
The slowdown appears to coincide with Russia reducing the number of air strikes against IS targets, IHS has observed.
At the start of the year, some 26% targeted IS, but by the summer it had dropped to just 17%.
Interactive See how the area IS controls has changed since 2015
"Last September, President Putin said it was Russia's mission to fight international terrorism and specifically the Islamic State," said Alex Kokcharov, principal Russia analyst at IHS. "Our data suggests that is not the case.
"Russia's priority is to provide military support to the Assad government and, most likely, transform the Syrian civil war from a multi-party conflict into a binary one between the Syrian government and jihadist groups like the Islamic State; thereby undermining the case for providing international support to the opposition."
Yet the losses the group has sustained are still significant, experts say. IS has been pushed back 10km from the Turkish border, while Iraqi forces have secured Qayyarah Airbase, a key strategic facility 60km south of the IS stronghold of Mosul.
It also lost the Syrian city of Manbij and its surrounding roads, which linked the Turkish border to IS' de-facto capital Raqqa, to US-backed Kurdish and Arab fighters in August.
"The Islamic State's territorial losses since July are relatively modest in scale, but unprecedented in their strategic significance," said Columb Strack, senior analyst and head of the IHS Conflict Monitor.
"The loss of direct road access to cross-border smuggling routes into Turkey severely restricts the group's ability to recruit new fighters from abroad, while the Iraqi government is poised to launch its offensive on Mosul."
Should the long-promised and much-delayed offensive against Mosul - expected to begin later this month - be successful, it would be a huge blow the extremists.
Mosul - Iraq's second city, under the control of the extremists since 2014 - is described as the "last bastion" for IS in Iraq, with authorities in Baghdad saying it would spell the end for the group in their country.