Thick black smoke was spotted billowing from the chimney of the Russia consulate in San Francisco on Friday, a day after Washington ordered it to be closed as part of ongoing tit-for-tat exchanges.

Firefighters who arrived at the scene were turned away by occupants who said there was no emergency and that they simply had a fire in the fireplace.

Staff have been given a Saturday deadline to close the consulate.

So what could they be burning when temperatures in San Francisco tipped 35C outdoors?