Former director of public prosecutions Grenville Cross has dismissed criticism of Hong Kong's National Security Law (NSL) as "unmerited", claiming they are made to "justify hostile political agendas against China".

Speaking on RTHK's NSL Chronicles II programme on Sunday, Cross said he believed that stringent laws such as the NSL are needed to deter terrorism and facilitate police investigations.

But he also said the NSL is more lenient than internal security laws in Singapore and Malaysia, which allow authorities to detain suspects indefinitely.

Cross told the programme that the law protects the judicial rights of defendants, with the International Covenant on Civil and Political Rights specifically mentioned in Article 4 of the legislation.

"The National People's Congress went that extra mile by incorporating that, so that everyone will be aware the new legislation is not intended to erode the judicial rights in our common law jurisdictions," the former prosecutions head said.

Cross also urged youngsters to behave responsibly online, saying proper education in schools is important to teach youngsters basic moral values.