BAGHDAD -- US Defense Secretary Ashton Carter arrived here on an unannounced visit to meet with Iraqi leaders as the Iraqi forces are fighting to defeat the Islamic State (IS) militants from their last major stronghold in Iraq, al-Arabiyah television reported on Saturday.

Carter is expected to meet with Iraqi Prime Minister Haider al-Abadi and other top officials and military commanders to discuss the Iraqi offensive against the extremist IS group in Mosul, the channel said.

Hundreds of US troops are already in Iraq, serving as trainers and advisers, in an attempt to help the country win the battle against IS militants in the country's northern city of Mosul.

The US-led international coalition has also been conducting air raids against IS targets in both Iraq and Syria.

Carter's visit came as the Iraqi security forces backed by anti-IS international coalition are carrying out a major offensive to drive out the IS militants from its last major stronghold in and around Mosul in northern Iraq.

On Oct 17, Iraqi Prime Minister Haider al-Abadi, who is also the commander-in-chief of the Iraqi forces, announced the start of a major offensive to retake Mosul, the country's second largest city.

Mosul, some 400 km north of the Iraqi capital of Baghdad, has been under IS control since June 2014, when Iraqi government forces abandoned their weapons and fled.