Turkish President Recep Tayyip Erdoğan declared he would resign if it is proven that Turkey ever purchased oil from the Islamic State (ISIS/ISIL), following claims by the Russian government that they have found proof of transactions.

“As soon as such a claim is proved, the nobility of our nation requires [me] to do this,” he said the world at the Paris climate change summit. “I will not remain in this post. But I am asking Mr. Putin, would you remain?”

The declaration comes after Putin accused Turkey of purchasing oil from the radical Islamic group.

“At the moment we have received additional information confirming that that oil from the deposits controlled by Islamic State militants enters Turkish territory on industrial scale,” stated Putin. “We have every reason to believe that the decision to down our plane was guided by a desire to ensure security of this oil’s delivery routes to ports where they are shipped in tankers.”

In October 2014, David Cohen, the undersecretary for terrorism and financial intelligence, said in a speech to the Carnegie Endowment for International Peace that ISIS earns “as much as $1m a day through the sale of oil to some of its biggest enemies: middlemen from Turkey, Iraq’s Kurdish community and the regime of Bashar al-Assad.” From his speech:

So who, ultimately, is buying this oil? According to our information, as of last month, ISIL was selling oil at substantially discounted prices to a variety of middlemen, including some from Turkey, who then transported the oil to be resold. It also appears that some of the oil emanating from territory where ISIL operates has been sold to Kurds in Iraq, and then resold into Turkey. And in a further indication of the Asad regime’s depravity, it seems the Syrian government has made an arrangement to purchase oil from ISIL.

It is difficult to get precise revenue estimates on the value to ISIL of these transactions in light of the murky nature of the market, but we estimate that beginning in mid-June, ISIL has earned approximately $1 million a day from oil sales.

There are good indications, however, that recent coalition military efforts have begun to impair ISIL’s ability to generate revenue from oil smuggling. Airstrikes on ISIL oil refineries are threatening ISIL’s supply networks and depriving it of fuel to sell or use itself. Moreover, our partners in the region, including Turkey and the Kurdistan Regional Government, are committed to preventing ISIL-derived oil from crossing their borders. Last week, the International Energy Agency reported that ISIL’s ability to produce, refine and smuggle oil had been significantly hampered.

“We have made our position very clear on this issue,” retorted Tanju Bilgiç, spokesman for Turkey’s Ministry of Foreign Affairs. “Both minister of foreign affairs Mevlüt Çavuşoğlu and minister of energy Taner Yıldız have repeatedly denied that oil has been sold by [Isis] to Turkey.”

In July, a western official told The Guardian that evidence seized at the compound of Abu Sayyaf, an ISIS leader, indicated there were links between the terrorist group and the Turkish government.

“There are hundreds of flash drives and documents that were seized there,” explained the official. “They are being analysed at the moment, but the links are already so clear that they could end up having profound policy implications for the relationship between us and Ankara.”

ISIS placed Sayyaf in charge of oil smuggling, a multi-million-dollar industry for the terror group. The evidence at his compound allegedly highlights NATO member Turkey as one of their top clients.

Tensions between Turkey and Russia escalated after Nov. 24 when Turkish forces shot down a Russian warplane, killing one pilot. Turkish officials claim they sent the jet ten warnings demanding it identify itself and leave Turkish airspace, but Russian officials said none were received. The Turkish military released audio of the warnings sent to the Russian plane the following day. Russian officials dismissed the recordings as fabrications.