Britain has killed more than 1,700 Islamic State (IS) terrorists in air strikes in Iraq and Syria, according to official statistics.
Figures to the end of September obtained by the Press Association under Freedom of Information laws show an estimated 1,571 fighters recorded as having been killed in Iraq since bombing began two years ago, and 181 in Syria since the start of operations there in December 2015.
The Ministry of Defence said "detailed assessments" of the 1,066 air strikes the RAF has carried out against IS showed no civilians have been killed - a claim that if true would be "unprecedented in the history of modern warfare", according to a prominent monitoring group.
The spike in numbers killed in Syria during August (108), came as RAF Typhoons, Tornadoes and Reaper drones were assisting Kurdish-led rebel forces liberate the city of Manbij, in Aleppo province, from IS control.
The UK has been able to kill proportionately more militants in Iraq because it is operating there with the local government's support, and has been able to break many IS lines of communication in the country.
Defence Secretary Sir Michael Fallon said: "Daesh is being defeated. It is being driven back. It now occupies less than 10% of Iraqi territory.
"So two years on we're making significant progress. This remains a hard fight. Yet Britain will not waiver in our efforts to defeat the evil of our age."
The MoD said it cannot verify the number of IS extremists killed as it is unable to visit the air strike sites, adding: "They are estimated figures based on post-strike analysis."
The monitoring group Airwars said this "air-only" assessment of the damage RAF bombs cause means the Government cannot claim it has not killed civilians, and stressed this puts Britain in the same position as Russia on the issue.
Airwars director Chris Woods said the MoD had engaged with the organisation about the 35 incidents of concern it raised between January and July where there have been reports of civilian deaths, and RAF aircraft have been in the vicinity.
But he went on: "Where we have more concern with the MoD is its assertion, an aggressive assertion at times, that they have killed no civilians in the war in Iraq and Syria despite more than 1,000 air strikes.
"That would be unprecedented in the history of warfare.
"What they are really saying is, from their air-only surveillance, they do not know."
He went on: "The MoD is really saying it doesn't know, but from its own aerial assessments, the best it can say is it probably hasn't.
"That gets translated by ministers and civil servants as 'we have not killed any civilians'.
"That is a position which we do not recognise.
"From the air alone they cannot know the effect that their air strikes are having on the ground."
Mr Woods said the US is the only coalition power to admit killing civilians.
"Britain is in the uncomfortable position of being in the same position as Russia in claiming that large numbers of air strikes have killed no civilians," he added.
The MoD said RAF pilots operate under strict targeting procedures to minimise the risk of civilian casualties.
It is understood this includes an ability to "shift cold" mid-strike and direct missiles or other munitions away from a target if potential civilians enter an area where terrorists are being attacked.
"We can't completely eliminate the risk of civilian casualties but we carefully mitigate that risk through strict targeting procedures," a spokesman said.
"The evidence from detailed assessments of each strike is that we've avoided any civilian casualties so far in this conflict."
Shadow defence secretary Nia Griffith said: "I welcome the fact that RAF air strikes in Iraq and Syria appear to be having an impact on the number of Daesh fighters on the ground.
"Targeted air strikes carried out in accordance with international law clearly have an important role to play in combating Daesh's capability in Iraq and Syria, and its ability to carry out attacks in this country and elsewhere.
"It is of course essential that all reasonable precautions are taken to avoid civilian casualties."