°®Âþµº

Ashton Carter’s unannounced visit to talk with Prime Minister Haider al-Abadi is understood to be the fourth since February 2015.

"What I'll be discussing with Prime Minister Abadi and our commanders there are the next plays in the campaign, which involve the collapse and control over Mosul," Carter told reporters aboard a military plane ahead of his visit.

The ultimate goal, he added, was "the recapture of all of Iraqi territory by the Iraqi security forces, but of course Mosul is the biggest part of that."

The duo were met with the Canadian Defence Minister who also made the unexpected journey to Baghdad a few hours later, °®Âþµº correspondent in Iraq confirmed. 

It comes just two days after US-backed government forces recaptured an airbase to the south of Mosul – adding to a string of victories expected to aid in the long-awaited operation to push the Islamic State group from Mosul.

Prime Minister Haider al-Abadi described the Qayyarah airbase as an "important base to liberate Mosul" calling on the city's residents "to get ready for the liberation of their areas."

Several important cities across the two countries, including Ramadi in Iraq and al-Shadadi, a town in northeastern Syria previously considered a strategic IS stronghold have been recaptured in recent months – more than two years after the militants seized large swaths of land in Iraq and Syria.

But as the anti-IS coalition powered through militant-held cities in the region, all efforts have since refocused on Mosul, Iraq's second-largest city located about 360 kilometres (225 miles) northwest of Baghdad, which fell to militants during the summer of 2014.

Despite this, both Carter and US President Barack Obama have been criticised for the pace of the anti-IS campaign, which began in Autumn 2014 and got off to a slow start, particularly in war-torn Syria, where the United States had few assets on the ground to provide targeting information.