The US will send about 600 additional troops to Iraq to train local forces ahead of the Mosul offensive, which will commence later this year, to retake the city from Islamic State (Isis), US Defence Secretary Ashton Carter, said on Wednesday.

"These (US) forces will be primarily to enable Iraqi security forces, and also peshmerga, in the operations to isolate and collapse ISIL's control over Mosul," Carter said. This is the third time since April that the US will be sending additional military personnel to Iraq, which will take the number of US troops in the country to 5,000.

Carter added that Iraq and US "have agreed that additional US and coalition capabilities could help accelerate the campaign at this critical phase". The troops will assist Kurdish peshmerga and Iraqi forces in their offensive and will "protect and expand Iraqi security forces' gains elsewhere in Iraq", Carter explained.

IS (Daesh) occupied Mosul in June 2014, but Iraqi forces recaptured many areas from the militant group and are preparing to regain control of Iraq's second largest city.

The push to retake Mosul could begin in the second half of October, US and Iraqi commanders have hinted.

"We are prepared to continue to help the Iraqi security forces consolidate their control over the country. Mosul will be the last of the very large cities that needs to be recaptured, but they'll need to continue to consolidate control over the whole city," Carter noted.

The troops will be based at Qayyarah, a key air base about 40 miles (65km) south of Mosul, which Iraqi forces took back from IS in July. The base has now been turned into a logistics hub for the upcoming offensive. Other US troops will head to Ain al-Assad Air Base in western Iraq, where hundreds of US forces have been training Iraqi personnel.

Pentagon spokesperson Captain Jeff Davis said that the troops will be sent to Iraq in the coming weeks. According to Reuters, three US service members have been killed in direct battle since the US began its campaign against Isis.

Mosul offensive
Members of the Shia Badr Organisation train before the upcoming battle to recapture Mosul in Diyala province, Iraq on 27 September 2016 REUTERS/Stringer