BAGHDAD: The United States will send an additional 560 military personnel to Iraq to assist in its fight against the militant Islamic State (IS) group, visiting Defence Secretary Ashton Carter announced Monday.

The increase will bring the total authorised number of American forces in Iraq, most of whom are in advisory or training roles, to more than 4,600, further deepening Washington's military involvement.

“I am pleased to report today that we agreed for the United States to bolster Iraqi efforts to isolate and pressure Mosul by deploying 560 additional troops,” Carter said in Baghdad, referring to Iraq's IS-held second city.

“The additional troops will provide a range of support for Iraqi security forces, including infrastructure and logistical capabilities at the airfield near Qayyarah,” the Pentagon said in a statement on Carter's announcement.

Prime Minister Haider al-Abadi announced Saturday that Iraqi forces had recaptured the Qayyarah airbase, some 60 kilometres south of Mosul, which IS seized in June 2014.

The base “will become a vital springboard for the (Iraqi forces') offensive into Mosul”, the Pentagon said.

IS overran large areas north and west of Baghdad in 2014, but Iraqi forces backed by US-led air strikes, training and other assistance have since regained significant ground.

US-led forces invaded Iraq in 2003, overthrowing dictator Saddam Hussein and also setting the stage for 13 years of bloody violence in the country, including the rise of IS.

President Barack Obama hailed the withdrawal of US forces from Iraq at the end of 2011 as a major achievement of his presidency, but the war against IS has drawn the American military ever deeper back into Iraq.