THE HAGUE, Netherlands (AP) – Ukraine says it is investigating a claim that a poisonous substance was dropped on the besieged city of Mariupol. Deputy Defense Minister Hanna Maliar said Tuesday it was possible that phosphorus munitions – which cause horrendous burns but are not classed as chemical weapons – had been used. Now the question is how to establish the truth amid the fog of war that has descended over a city still under attack from Russian forces. The global chemical weapons watchdog said Tuesday it is “concerned by the recent unconfirmed report of chemical weapons use in Mariupol” and is closely monitoring the situation in Ukraine. But experts says it’s much too dangerous now to send an investigation team into Mariupol.