Some of Moscow's key allies rallied round Russian President Vladimir Putin on Tuesday on the first day of a major summit that the Kremlin hopes will show Western attempts to isolate it over the Ukraine offensive have failed.

Putin is hosting around 20 world leaders — including China's President Xi Jinping, India's Prime Minister Narendra Modi and Turkey's President Recep Tayyip Erdogan — for a three-day gathering of the BRICS group in the central city of Kazan.

The Kremlin leader wants to use the forum to challenge the West and advance his idea of a "multipolar world" as a bulwark against U.S. "hegemony."