Huang Nanhua was sentenced to 16 years in prison. Police caught him carrying a homemade pistol and ammunition at a roadblock last year, as well as pictures and addresses of the activists - veteran politician Martin Lee and media mogul Jimmy Lai, according to prosecutors during the trial.

Huang's visit to Hong Kong from mainland China was part of a plan "to teach someone a lesson," prosecutors said. The defence had argued Huang had no intention of hurting anyone and was visiting Hong Kong for a shopping trip.

Handing down the sentence Friday, Hong Kong judge Peter Line said he believed Huang "intended to commit a serious crime involving violence."

Lee, the popular founder of Hong Kong's pro-democracy party and one of the mainland's most vocal critics, did not seek re-election last year but campaigned aggressively for democratic candidates.

"I am not going to be intimated by this matter," Lee told reporters in footage aired on Hong Kong Cable TV. "It's not going to affect my work, whether in my quest for democracy or in my legal work."

Lee, who is a lawyer, said he did not know the defendant, suggesting the mastermind remained at large. Police would continue to investigate the case as they did not consider it to be closed, he added.

Lai, also considered a thorn in the side of Beijing, runs Hong Kong's mass market Apple Daily newspaper, known for its staunch pro-democracy line.