LONDON — Two weeks before the anniversary of a nerve-agent attack against a former Russian spy in Salisbury, England, someone unfurled a large Russian flag on the city’s cathedral overnight, in what residents took to be a mockery of the ordeal they suffered last year.

Images of the Russian flag, fluttering from scaffolding around the cathedral, were widely circulated on social media Sunday morning.

The dean of Salisbury, Nicholas Papadopulos, called it “a remarkably stupid thing to do.”

He said it “makes light of the huge personal tragedies involved, and the damage done to the city by the unprecedented nerve agent attacks on Salisbury last year.”

It was not clear who climbed the scaffolding surrounding the building to put up the flag, which was hastily removed Sunday morning. The flag has been handed over to the police, the cathedral said.