Police in England say 18-year-old suspect Axel Rudakubana is charged with producing the deadly poison ricin, and having an Al-Qaeda jihad training manual in his possession.

Cops say they found the ricin and the Al-Qaeda manual in searches of Rudakubana's home following the July Southport stabbings. Ricin, derived from castor bean plants, is considered one of the world's deadliest toxins.

While the new charges involve terror, police say the case has not been officially classified as a terrorist attack ... because motive would need to be established.

Rudakubana, who cops say was born in England, is scheduled to appear in court Wednesday ... and he's already been charged with murder, attempted murder, and possession of a knife.

As we reported ... Rudakubana is accused of fatally stabbing 3 children -- ages 6, 7 and 9 -- on July 29 at a Taylor Swift-themed dance workshop in the UK. Police say ricin was not found at the scene of the murders.

In an Instagram post after the attack, Taylor told her fans she was "completely in shock" ... "These were just little kids at a dance class. I am at a complete loss for how to ever convey my sympathies to these families."