Noxious gas is spreading throughout Moscow, and authorities have urged residents in certain parts of the city to stay indoors. Media reports say the gas is hydrogen sulfide, which smells like rotten eggs and can be highly toxic. The smell has been detected in the south, east, and southeastern part of the Russian capital, but no source of the gas leak has been confirmed yet. Interfax reported that Russia’s emergency ministry pinned the blame on a Moscow oil refinery. However, its owner, Gazprom Neft, responded that there were no accidents and hydrogen sulfide levels were not excessive.