"I love you," Alexei Navalny's wife, Yulia, posted on social media on Sunday beside a picture of them together.

The post on Instagram showed a picture of the two together, their heads touching as they watched a performance of some kind.

Navalny, a 47-year-old former lawyer, fell unconscious and died on Friday after a walk at the "Polar Wolf" penal colony in Kharp, about 1,900 km (1,200 miles) northeast of Moscow, where he was serving a three-decade sentence, the prison service said.

Western leaders led by U.S. President Joe Biden paid tribute to Navalny's courage and, without citing evidence, accused President Vladimir Putin of being responsible for the death. Britain said there would be consequences for Russia.

The Kremlin said the West's reaction was unacceptable and "absolutely rabid." Putin has yet to comment on Navalny's death.