Turkish President Tayyip Erdogan said on Friday that his Ukrainian counterpart’s comments about the need for a referendum on compromises with Russia were “smart leadership,” according to broadcaster NTV and others.

Erdogan told reporters on his way back from a NATO summit in Brussels that Turkey could not impose sanctions on Russia because of its energy needs and cooperation.

Ukraine’s President Volodymyr Zelenskiy said on Monday that any compromises reached with Russia to end the war would be subject to a referendum.

Erdogan said he would hold separate calls with Ukrainian and Russian counterparts in coming days to evaluate the summit.

NATO member Turkey shares a maritime border with Ukraine and Russia in the Black Sea, has good ties with both and has offered to mediate the conflict. While supporting for Ukraine and being critical of Russia, Ankara has opposed sanctions on Moscow.

“We are buying nearly half of the natural gas we use from Russia. Separately, we are making our Akkuyy Nuclear Power Plant with Russia. We cannot set these aside,” Erdogan said.

“So there is nothing that can be done here. We must maintain our sensitivity on this issue. Firstly, I can’t leave my people in the cold of the winter. Secondly, I cannot halt our industry. We must defend these,” he added.

He also said Ukrainian and Russian negotiators were able to agree on four out of the six main issues being discussed during peace talks, but that territorial disputes on the eastern region of Donbass and Crimea remained.