The opposition-held sector of Syria’s divided city of Aleppo has been cut off from the outside world in recent days by an escalation of air and artillery strikes on the only road in, putting hundreds of thousands of people under effective siege.

A government campaign to fully capture Aleppo would most likely bury what little hope remains of reviving a diplomatic effort to end the five-year-old civil war, after talks and a ceasefire sponsored by the United States and Russia fell apart earlier this year.

Russia said last week its air force would provide “the most active” support to prevent Aleppo and the surrounding area falling into the hands of what it called terrorists, a word Moscow and Damascus use to describe an array of Assad’s enemies.