Pentagon chief Ashton Carter arrived in Baghdad Monday for talks with Prime Minister Haider al-Abadi on the fight against the Islamic State group and plans to recapture Mosul from the jihadists.

Carter's unannounced visit -- his fourth to Iraq since beginning his job in February 2015 -- comes two days after Iraqi forces captured an airbase to the south of Mosul that is seen as an important step toward the eventual battle for the country's second city, which has been under IS control since June 2014.