Russian President Vladimir Putin dropped a bombshell when he revealed that the Islamic State (ISIS) is being financed by private donors from at least 40 countries, including some G-20 member states.

The Russian leader made the disclosure at the Group of 20 summit in Antalya, Turkey, where the fight against ISIS topped the discussion. He claimed to have exchanged intelligence with other member states and discovered that the terror group—which is now the object of massive airstrike campaigns by Russia and the U.S.-led coalition—is actually getting funding support from private individuals from these countries, and surprisingly even from some G-20 members.

"I provided examples based on our data on the financing of different Islamic State units by private individuals. This money, as we have established, comes from 40 countries and, there are some of the G-20 members among them," Putin told journalists, Rawstory.com reported.

Putin did not specify the countries although unconfirmed reports said the extremist group has donors in Arab countries such as Kuwait, Qatar and Saudi Arabia.

During the two-day summit, the Russian president also reportedly warned other member states about the dangers of the illegal trade in oil with ISIS.

"I have shown our colleagues photos taken from space and from aircraft which clearly demonstrate the scale of the illegal trade in oil and petroleum products. The motorcade of refuelling vehicles stretched for dozens of kilometres, so that from a height of 4,000 to 5,000 metres they stretch beyond the horizon," Putin said.

U.S. and Iraqi intelligence officials say that ISIS makes about $50 million a month from selling crude from captured oilfield in Iraq and Syria.

A report by Business Insider said: "Oil sales—the extremists largest single source of continual income—are a key reason they have been able to maintain their rule over their self-declared caliphate stretching across large parts of Syria and Iraq.''

"With the funds to rebuild infrastructure and provide the largesse that shore up its fighters' loyalty, it has been able to withstand ground war against its opponents and more than a year of bombardment in the U.S.-led air campaign."

Putin appealed to the international community to come together to fight ISIS.

However, some countries have raised concerns that Russia's motive is to bolster the regime of President Bashar Assad.

"Some armed opposition groups consider it possible to begin active operations against ISIS with Russia's support and we are ready to provide such support from the air. If it happens it could become a good basis for the subsequent work on a political settlement. We really need support from the U.S., European nations, Saudi Arabia, Turkey, Iran,'' he said.

On Sunday, Putin met privately with U.S. President Barack Obama to discuss a strategy for conflict resolution in Syria.

The two countries have announced their commitment to fighting ISIS, but have conflicting policies in Syria.