The so-called Islamic State group is facing its “end game” in the Iraqi city where its campaign of violence began in 2014, the defence secretary has said.
Sir Michael Fallon said the RAF had hit more than 700 targets in support of the liberation of Mosul by Iraqi forces.
IS is also losing ground in its Syrian stronghold of Raqqa, Sir Michael said.
He was speaking before a Nato meeting where he is expected to confirm 85 more UK troops will be sent to Afghanistan on training duties.
There are already 500 British personnel in the country.
The US-led coalition against IS has been stepping up airstrikes in recent months, with the RAF now working at its highest operational tempo in 25 years.
UK forces have also hit 69 targets in support of Syrian Democratic Forces in Raqqa, where Sir Michael said there is “irreversible momentum and progress” towards the defeat of IS.
The UK has also been using “offensive” cyber attacks against IS.
The Ministry of Defence said the UK commitment to the Afghan training mission was part of a global effort to counter terror and build stability.
Sir Michael Fallon said: “Keeping Afghanistan from becoming a safe haven for transnational terrorists helps to keep our streets safe too.
“That’s why we’re stepping up our support to the government of Afghanistan and its defence forces, helping them to expand security and develop their armed forces.”