The booksellers all worked for the same Hong Kong-based publishing house and are feared to have been detained by Chinese authorities, adding to growing unease that freedom in the semi-autonomous city is being eroded.
Under its mini-constitution, Hong Kong enjoys freedom of speech and Chinese law enforcers have no right to operate in the city.
Leung Chun-ying told reporters: “The government cares very much about Hong Kong residents’ rights and safety.”
Leung said freedom of press, publication and expression was protected under Hong Kong law.
“Only legal enforcement agencies in Hong Kong have the legal authority to enforce laws in Hong Kong,” he added.
Not going far enough
Democratic legislator Albert Ho said on Sunday he believed the men had been kidnapped by Chinese security officers.
But when Leung was asked on Monday whether he thought the men had been taken to the mainland, he said there was “no indication” and appealed for anyone with information to come forward.
It is still unclear where the men are or how they went missing.
Unpopular Leung is seen as close to Beijing and is a hate figure for pro-democracy activists.
Opponents criticised him for not going far enough to press Chinese authorities for information.
“The Hong Kong government and Leung Chun-ying should express to the top level on the mainland Hong Kong people’s concern, instead of awaiting a reply,” said pro-democracy lawmaker Lee Cheuk-yan.