In March 2019, Wang purchased some sodium nitrite after being involved in a dispute with a fellow teacher.

A former lawyer who rose to prominence by lampooning President Vladimir Putin's elite and voicing allegations of corruption on a vast scale, Navalny has long forecast Russia could face seismic political turmoil.

Scores of Iranian schools have been hit by poisonings since late November, with pupils suffering symptoms ranging from shortness of breath to nausea and vertigo after reporting 'unpleasant' odours on school premises.