By Clare Baldwin

HONG KONG (Reuters) - Candidates in an election in Hong Kong in September must pledge that the city is an "inalienable" part of China, and anyone who advocates independence could be banned from standing, the head of the Electoral Affairs Commission (EAC) said.

EAC chairman Justice Barnabas Fung Wah made his comments after the commission and the Hong Kong government drew anger by saying that candidates for the legislative council -- which includes pro-democracy and independence activists -- were required to declare in a new Confirmation Form that Hong Kong falls directly under the central government in Beijing.

The Hong Kong government also said that advocating and promoting independence was "contrary" to that declaration and could render a candidate ineligible. The EAC said anyone making a false declaration was "liable to criminal sanction".

Hong Kong is part of China but governed by separate laws under a "one country, two systems" framework agreed with Britain when it was handed back from colonial rule in 1997.

"The introduction of the Confirmation Form has sound legal basis. The measure (is) entirely based on legal and procedural considerations," Fung told lawmakers on Tuesday, according to a printed version of the remarks.

Relations between Hong Kong and Beijing have frayed in recent years over pro-democracy protests, a failed bid for electoral reform, and instances where Hong Kong residents say Beijing is breaking the "one country, two systems" agreement - such as the alleged abduction of five Hong Kong booksellers known for their gossipy books about China's leaders.

There is also a small but vocal minority of activists calling for outright independence.

"There have been comments and proposals in the public arena which have deviated from 'one country, two systems' and the constitutional status of Hong Kong as prescribed in the Basic Law. In this regard, there are public concerns on whether candidates fully understand the Basic Law," Fung said.

Beijing's chief representative in Hong Kong, Zhang Xiaoming, said in a separate speech on Wednesday that allowing independence activists to run for office - or even use the election as a platform for their ideas - would be a breach of the "one country, two systems" framework, public broadcaster RTHK reported.

A candidate who fails to submit the Confirmation Form may be asked for further information and election officers, with input from the Justice Department, may declare the candidacy invalid, according to the EAC.

The EAC is an independent statutory body that oversees elections in Hong Kong. Legislative Council elections are on Sept. 4.

(Reporting by Clare Baldwin; Editing by Michael Perry and Angus MacSwan)