WASHINGTON (BLOOMBERG) - The United States is "deeply concerned" about 12 Hong Kong pro-democratic activists held in mainland China who have been denied access to lawyers of their choice, according to Secretary of State Mike Pompeo.

The activists were arrested two weeks ago off the coast of Hong Kong by Guangdong Maritime Police.

Local authorities haven't provided information on their welfare or charges against them, Mr Pompeo said in a statement on Friday (Sept 11).

He also questioned Hong Kong leader Carrie Lam's commitment to protecting the rights of her residents and called on the authorities to ensure due process.

At a press conference in Hong Kong on Saturday, family members of six of the activists urged the authorities to allow their own lawyers, instead of government-appointed ones, to meet the detainees.

The family members said they hadn't heard from the activists, and urged mainland officials to allow contact.

They called on the Hong Kong government, which they said hadn't provided them with any "concrete help", to get the activists back.

One of the detained is 16 years old while at least two need prescribed medication, Hong Kong pro-democracy lawmaker Eddie Chu said at the briefing.

Mrs Lam said on Tuesday that it's "not a question of simply getting them back", because if Hong Kong residents were arrested for breaching mainland offences, they have to be handled under the mainland law.

The Hong Kong government will provide assistance to those residents if needed, she said.