US Defence Secretary Ashton Carter arrived in Baghdad Saturday to review the six-day-old offensive to retake Mosul, the Islamic State group's last major stronghold in Iraq.

He will meet commanders from the 60-nation coalition which is led by the United States and assists Iraqi forces in their drive against the jihadists.

Carter is also due to meet Iraqi Prime Minister Haider al-Abadi and is expected to discuss Baghdad's objections to Turkish involvement in the Mosul operations.