Iraqi Kurdish forces are a key US partner in the war against IS, which overran large parts of Iraq last year.

Carter met with Iraqi Kurdish leader Massud Barzani during the visit to Arbil, the capital of the autonomous Kurdish region.

Carter had travelled to Baghdad the previous day.

There, he met Prime Minister Haider al-Abadi, and the two discussed "improving cooperation between the two countries in the fields of arming and training," a statement from the premier's office said.

Carter and his delegation also met US partners in the international anti-IS coalition.

US aircraft carry out daily air strikes against IS targets, most of them in the Iraqi part of the jihadists' self-proclaimed "caliphate", which also covers regions in Syria.

Coalition aircraft carried out 11 strikes in Iraq on Wednesday, four of them in the area of the Anbar provincial capital Ramadi, which Baghdad's forces are battling to retake from IS.

President Barack Obama said on Monday the US and its allies were hitting IS "harder than ever" and warned the extremists' leaders: "You are next."