WASHINGTON (DPA) - US President Donald Trump has declared his intention to wind down his country's 2,000 troops in Syria, but a report issued on Monday (Feb 4) warned the extremist group could then make a comeback within six to 12 months.

The report by the inspector general of the Department of Defence warned that the Islamic State in Iraq and Syria militant group continues to attract dozens of foreign fighters to Syria and Iraq each month, and maintains a flow of external donations.

Islamic State is "regenerating key functions and capabilities more quickly in Iraq than in Syria."

In both Syria and Iraq, local forces remain heavily reliant on support from the US-led coalition, the report said.

While singling out the Kurdish-led Syrian Democratic Forces (SDF) as "tenacious fighters", the inspector general noted the threat of a Turkish invasion against these US-backed forces, as Ankara views them to be linked to Turkish separatists.

The SDF's war against Islamic State in Syria continues.

Islamic State maintains some 2,000 fighters in eastern Syria where it has established strong defensive positions and will likely fight on until the last man.

"Challenges to completely defeating ISIS in Iraq include the group's rural strength, its tunnels and safe houses, the continued trickle of foreign fighters, the difficulty in securing the Iraq-Syria border, and the lack of stability in Sunni areas," the report said.

The report noted, positively that this year's Shiite pilgrimages were conducted without major terrorist attacks by Islamic State - an extremist Sunni group.