U.S. Defense Secretary Ash Carter says the U.S. has made progress against the Islamic State group in Iraq but cannot predict how long the fight will take.

Speaking at a joint news conference with his South Korean counterpart, Carter said he would not go so far as to say this is the beginning of the end for IS in Iraq.

Carter also said the Pentagon is not yet ready to discuss with Seoul the possibility of deploying an advanced US missile defense system in South Korea.

Later Carter was flying to a South Korean naval base and visiting a seaside memorial to the 46 South Korean sailors who died in the 2010 sinking of the Cheonan, which Seoul says was caused by a North Korean torpedo.