Jihadist leader Abu Bakr al-Baghdadi called on his fighters to resist as Iraqi forces were poised Thursday, November 3 to enter the city of Mosul where he declared a "caliphate" two years ago, AFP reports.

The appeal was made in an audio recording released on the Internet and purported to be by the elusive leader of the Islamic State group, his first message this year.

"Do not retreat," he said. "Holding your ground with honour is a thousand times easier than retreating in shame."

"To all the people of Nineveh, especially the fighters, beware of any weakness in facing your enemy," Baghdadi said, referring to the northern Iraqi province of which Mosul is the capital.

In June 2014, days after jihadist fighters swept across swathes of Iraq, he made a rare public appearance in Mosul and announced the creation of an Islamic "state" straddling Iraq and Syria.

The "caliphate" has been shrinking steadily since last year and Iraqi forces earlier this week reached Mosul, the jihadists' last major stronghold in Iraq.

Tens of thousands of Iraqi forces, backed by the U.S.-led coalition and its warplanes, launched a massive offensive on Mosul on October 17.

It was not immediately possible for AFP to authenticate the recording, entitled "This is what God and his messenger have promised us", but leading experts of the jihadist organisation did not appear to doubt it.