The UK is to send an extra 125 military trainers to Iraq to help in the battle against Islamic State, the PM has said.
David Cameron made the announcement at the G7 in Bavaria, ahead of a meeting with the Iraqi leader on Monday.
Mr Cameron said that IS terror activity was "the biggest threat" G7 leaders had to address.
The latest pledge will take the number of UK personnel training Iraqi security forces to more than 275, but No 10 dismissed claims of "mission creep."
A spokesman said the additional help was being given at the request of Iraqi Prime Minister Haider al-Abadi.
Most of the extra personnel will be involved in training Iraqi soldiers to deal with explosive devices.
"I think the biggest challenge that we face in terms of the effect on Britain and the challenge in the world is fighting extremist Islamist terror, particularly obviously in Iraq and Syria, but more broadly," said Mr Cameron.
"We're already the second largest contributor in terms of air strikes in Iraq. We're providing a whole host of support to the Syrian opposition.
'Right thing to do'
"We already have quite a number of people in the KRG (Kurdistan Regional Government area), but these people will be helping more broadly in Iraq.
"It's a particular request that the Abadi government has made. It's a particular thing that we've been working with the Americans on. I think it's the right thing for Britain to do."
Downing Street said the new deployment would begin "shortly".
The bulk of the extra personnel - around 100 of those deployed - will train local forces in detecting and dealing with the roadside bombs and booby-trap explosives used by IS.
Another 25 will focus on logistical challenges, such as bridge-building.
The UK government first announced in March that it planned to send nearly 60 Army personnel to Iraq to help deliver training for Kurdish forces fighting IS.
The team were also sent to focus on the counter-IED training programme organised by the coalition fighting IS.
More than 1,000 Kurdish troops have already been trained by UK personnel.
While Britain's mission in Iraq has so far been largely focused on the region of Kurdistan's capital, Irbil, the extra personnel will be stationed at a number of bases around the country, including Baghdad.
It is understood they will remain inside bases and will not be deployed in the field.
The announcement came as Mr Cameron met US President Barack Obama on the margins of the G7 summit for talks expected to focus on defence issues.
Washington is concerned that UK spending on defence may drop below the Nato target of 2% of GDP.
Asked what he would tell Mr Obama about Britain's plans for future defence spending, Mr Cameron told reporters: "I'll say exactly the same as what I'm saying now, which is we've kept our 2% promise - one of the few countries to do it - and we're having a spending review in the autumn and we'll announce the results at that time."