Turkish President Tayyip Erdogan on Thursday dismissed “emotional” and “unfitting” suggestions that projects with Russia could be canceled following Turkey’s downing of a Russian warplane near the Syrian border.

In an escalating war of words, he responded to Russian accusations that Turkey has been buying oil and gas from Islamic State in Syria by accusing Syrian President Bashar al-Assad and his backers, which include Moscow, of being the real source of the group’s financial and military power.

The downing of the jet on Tuesday was one of the most serious publicly acknowledged clashes between a NATO member and Russia for half a century, and further complicated international efforts to battle Islamic State militants in Syria.

Russian Prime Minister Dmitry Medvedev ordered his government on Thursday to draw up measures that would include freezing some joint investment projects and restricting food imports from Turkey.

“We are strategic partners … ‘Joint projects may be halted, ties could be cut’? Are such approaches fitting for politicians?,” Erdogan said in a speech to local officials in the capital Ankara.

“First the politicians and our militaries should sit down and talk about where errors were made and then focus on overcoming those errors on both sides. But instead, if we make emotional statements like this, that wouldn’t be right.”

Erdogan said the Russian jet was shot down on Tuesday as an “automatic reaction” to the violation of Turkish air space, in line with standing instructions given to the military.

Those instructions were a separate issue to disagreements with Russia over Syria policy, he said, adding Ankara would continue to support moderate rebels in Syria and Turkmen fighters battling President Bashar al-Assad.

Russia insists its jet never left Syrian air space.

Medvedev on Wednesday alleged that Turkish officials were benefiting from Islamic State oil sales, while Russian Foreign Minister Sergei Lavrov said it was no secret that “terrorists” use Turkish territory.

“Shame on you. It’s clear where Turkey buys its oil and gas … Those who claim we are buying oil from Daesh like this must prove their claims. Nobody can slander this country,” Erdogan said, using an Arabic acronym for Islamic State.

“If you are seeking the source of weaponry and financial power of Daesh, the first place to look is the Assad regime and countries that act with it,” he said. Reuters