By Suzan Fraser and Ayse Wieting, SFGate

Ties between Russia and Turkey are growing closer than ever, as Russia runs into widespread diplomatic fallout from the poisoned spy scandal and Turkey’s relations with its Western allies worsen over human rights issues and its military operations against Kurdish militia in Syria.

Russian President Vladimir Putin heads back to Turkey on Tuesday, joining Turkish President Recep Tayyip Erdogan at a symbolic ground-breaking ceremony for a Russian-made nuclear power plant being built on Turkey’s Mediterranean coast at Akkuyu. On Wednesday, Putin, Erdogan and Iranian President Hassan Rouhani are expected to hold a summit in the Turkish capital of Ankara to discuss Syria’s future.

Turkey and Russia have put aside their traditional rivalries and differences on regional issues to forge strong economic ties. In December, they finalized an agreement for Turkey to purchase Russia’s long-range S-400 missile defense system, a deal that raised eyebrows among some of Turkey’s NATO allies. Aside from the power plant, the two countries are also building the “Turkstream” pipeline to transport Russian gas to Turkey.

The cooperation comes despite their positions on opposing sides in the Syrian conflict —with Moscow siding with Syrian President Bashar Assad and Turkey supporting his foes since the start of the Syrian war seven years ago.