LONDON—A man accused of launching a knife attack at a London subway station appeared in court on Monday, where prosecutors described the incident as an act of terrorism.

Muhaydin Mire, 29 years old, had been charged overnight with attempted murder after allegedly carrying out the attack on Saturday at Leytonstone station in east London, which left a victim with serious wounds and requiring surgery for a gash to his throat, according to the indictment.

At...