The Islamic State extremist group has about $ 300 million after the loss of its so-called "caliphate" in Iraq and Syria, according to a report by UN Secretary-General António Guterres, quoted by The Associated Press.

In a document sent to the UN Security Council, Guterres warns that the lull in IS attacks “may be temporary.”

Although the loss of territories has stopped the jihadist group from earning from oil sales, it has sufficient funds to finance terrorist attacks in Iraq, Syria and other countries, the report shows.

Guterres points out that the most common method of financing an organisation is through informal money transfers. Another possible source of funds is looted artefacts from ID-owned territories. According to the UN Secretary-General, the terrorist organisation is also promoting the financial self-sufficiency of its network of supporters and followers in the Middle East, Africa and Asia.

Mr Guterres said the evolution of a covert ISIS network in Iraq at the provincial level since 2017 is being mirrored in Syria, with attacks increasing in government-controlled areas, The Straits Times reported.

The report also draws attention to existing concerns about the return of foreign ID fighters to their home countries. According to several unnamed countries, about 25 percent of foreign fighters have been killed and 15 percent are unaccounted for.

"Set against an approximate initial figure of 40,000 who joined the 'caliphate,' these percentages would suggest that between 24,000 and 30,000 foreign terrorist fighters are alive," the report said.