Somalia has one year to expel the al Qaeda-linked al Shabaab militant group from the country, President Hassan Sheikh Mohamud said on Tuesday, with the deadline for remaining African Union peacekeepers to leave looming next December.

Al Qaeda-linked Al Shabaab has been waging a brutal insurgency against the Somali government since 2006 in a bid to establish its own rule based on a strict interpretation of Islamic Sharia law.

Mohamud, serving his second term as president, said in August he wanted to eliminate it by early next year.

"The end game is Dec 2024 when all the ATMIS (the African Union peacekeeping) forces have to leave the country," Mohamud told an audience at London's Royal United Services Institute.

The focus was on eliminating "the residual" al Shabaab, he said. That task had been made more difficult by recent deadly flooding, he said, although the floods have also made it harder for the militants to spread landmines.

Mohamud's recent drive against al Shabaab began in August last year, with the military rallying behind clan-based militias in central Somalia.

That rare collaboration helped produce the most significant territorial gains against the militants since the mid-2010s, but al Shabaab has continued to stage deadly attacks against military and civilian targets.

The most recent phase is meant to push into southern Somalia, the traditional stronghold of al Shabaab.

Mohamud described progress as "encouraging," adding that there were no indications at present that al Shabaab's leaders wanted any dialogue with the government.

"If that changes we will," he said. "I believe this will end up in dialogue ... rather than killing and maiming and chasing away."

He said there was an acute need for the international community to help Somalia with its military efforts and to build up its state institutions, provide basic services such as health and education, and reconstruct its infrastructure.

The country has also over the years experienced bouts of drought and floods that have led to thousands being displaced.

Earlier this month, Somalia got preliminary approval from the International Monetary Fund (IMF) for a 100 million U.S. dollars, 36-month support programme.