Turkey has challenged Russia to prove its claim that Ankara shot down a Russian plane in order to protect its oil trade with Islamic State(IS). "If you allege something you should prove it," Turkish President Recep Tayyip Erdogan said. He was responding to a statement by Russia's President Vladimir Putin. Russia says Turkey downed the jet as it was flying over Syria. Turkey says the plane entered its airspace and was warned to leave. One Russian pilot was killed and the other rescued after Russia's Su-24 bomber was shot down by a Turkish F-16 fighter on the Syrian border on 24 November. A Russian marine was killed during the rescue operation in north-western Syria. Russia has insisted the plane did not cross the border and that it gave advance notice of the flight path to the US, Turkey's ally. But the US has supported Turkey's version of events. On Monday state department spokeswoman Elizabeth Trudeau said that "evidence from Turkey and our own sources indicates that Russian aircraft violated Turkish airspace", She added that Russia had not informed the US or its coalition of its air operation. "We do not co-ordinate operations with the Russian Federation," she said. "You should put your documents on the table if you have any. Let's see the documents," Mr Erdogan said. "We are acting with patience. It is not positive for the two countries which have reached a position which could be regarded as a strategic partnership to make emotional statements." President Erdogan also vowed to step down if the allegation that Turkey was buying oil from IS proved true, suggesting that President Putin should do the same if he was wrong. Russia has been carrying out air strikes in Syria, targeting rebels against Syrian President Bashar al-Assad, including IS.