Moscow ? An apparent explosion derailed several cars on a Russian passenger train traveling from Moscow to St. Petersburg late Monday, injuring at least 27 people, officials said.

The train’s driver heard a loud bang from underneath the locomotive immediately before it derailed near the city of Novgorod, about 300 miles northwest of Moscow, Alexander Pirkov, an adviser to Russian Railways’ top executive, said in televised comments.

Investigators were trying to determine what caused the 12 cars and locomotive of the “Nevsky Express” to derail, Pirkov said. The train was carrying 215 passengers and 20 crew, he added.

A statement posted later on the Russian Railways Web site said only that it was due to “illegal interference in the operations of railway transportation.”