HONG KONG (Reuters) - A second local activist in Hong Kong has been disqualified from running in next month's Legislative Council elections after declining to sign a new form saying the city is an "inalienable" part of China.

Yeung Ke-cheong, member of the Democratic Progressive Party, said in a Facebook post on Sunday that he had been barred, a day after Chan Ho-tin, a member of the Hong Kong National Party had also been disqualified.

Hong Kong's Legislative Council plays a key role in scrutinizing bills, control public expenditure and handles complaints from the public. The election is being closely watched to see if pro-democracy candidates will be able to secure seats.

Chan received an email from the Electoral Affairs Commission on Saturday which said his application to join the election had been "invalidated", fuelling speculation that others who hold pro-independence views also could be disqualified.

"The National Party is honored to become the first party to be banned from joining a democratic election by the government due to political difference," the party wrote on its Facebook page.

The requirement that candidates pledge that the former British colony is part of China, and that advocating independence could make them ineligible to stand for election, is the latest in a series of issues that have raised concern about what many people in Hong Kong see as mainland China's increasing control.

Hong Kong returned to Chinese rule in 1997 under a "one country, two systems" formula meant to guarantee the financial hub's considerable freedoms and separate laws.

But China's refusal to allow unfettered democracy in next year's election for the city's leader triggered pro-democracy protests in 2014, and spurred worries about the city's future.

A series of issues since then has compounded those fears.

The government issued a statement saying it agreed to and supported the decision to disqualify Chan.

The activists are one of a number of pro-independence candidates who refused to sign the recently introduced additional declaration form.

Previously, candidates only needed to pledge to uphold Hong Kong laws.

A Hong Kong court declined to rule on Wednesday on a challenge filed by activist politicians to the new rule.

About 100 people joined a rally on Saturday night to support Chan.

(Reporting by Anne Marie Roantree and Farah Master; Editing by Kim Coghill and Alison Williams)