Islamic State terrorists are completely "trapped" and "the last road out of Mosul" has been cut off, claimed a US envoy Sunday in Baghdad.

"Just last night, the 9th Iraqi army division, up near Badush, just northwest of Mosul, cut off the last road out of Mosul," news agency quoted US envoy to the anti-IS coalition Brett McGurk as saying.

Meanwhile, Iraqi government forces have expelled IS fighters from about 30 per cent of western Mosul, a senior official from the elite Counter-Terrorism Service(CTS) said on Sunday, a major progress in the massive operation to retake the second largest city of Iraq.

The official said that CTS soldiers clashed fiercely with IS members in the old city centre in western Mosul, stressing that the enemy's power has been greatly weakened in the battle.

Iraqi government forces launched the offensive to liberate western Mosul on February 19 after declaring the full control of eastern Mosul late January.

McGurk also announced that Iraqi Prime Minister Haider al-Abadi will visit Washington next week to hold discussions with US President Donald Trump on the further cooperation between two countries.