The world's most northerly forests could be a "time bomb" of planet-warming pollution as expanding wildfires have released record high levels of planet-heating pollution into the atmosphere, according to a new study.

Russian security officials claimed on Thursday that a small Ukrainian armed group had crossed the Russian border into the southern Bryansk region, allegations dismissed by Kyiv as a "classic deliberate provocation" by the Kremlin.

Demonstrators poured into the streets of Greece after a head-on collision between two trains killed dozens and left scores injured, amid anger over country's poor record on railway safety.

Ukrainian authorities are accusing Russia of trying to export an unlikely phenomenon: teenage gangs inspired by a Japanese anime game who are taking to the streets for mass brawls.