ASEAN Secretary-General Le Luong Minh has rebutted Beijing's questioning of his and the grouping's neutrality following his remarks that China had to leave Vietnam's territorial waters amid an escalating South China Sea dispute.

"The secretary-general's neutrality does not prevent him from expressing his views about developments impacting Asean member states even if such a member state happens to be his own country," Mr Minh, formerly Vietnam's deputy foreign minister, told The Straits Times in an e-mail last night.

He added: "Neutrality does not mean standing in the middle between right and wrong, rather at the middle of truth and of the shared interests of the organisation he is mandated to serve."

Chinese Foreign Ministry spokesman Hong Lei on Monday condemned Mr Minh for saying Asean had to "get China out of the territorial waters" of Vietnam to restore confidence and a conducive environment for formal talks between Asean and China on the South China Sea issue.

Mr Hong said these comments were not consistent with the role of the secretary-general, saying Mr Minh had "violated Asean's neutrality by unilaterally advocating another country's stand and sending the wrong signal to the world".

In his reply, Mr Minh said he had always been a strong supporter of Asean-China ties and cooperation, in which the South China Sea was not the only issue. But this issue had to be resolved amicably in the shared interests of both Asean and China, and turning away from it will not achieve such a solution.

"The secretary-general of Asean is accountable to the member states of Asean and the spokesperson of the Chinese foreign ministry is in no qualified position to pass official judgment of his mandate," he added.

Mr Minh also rejected Mr Hong's remarks that the South China Sea issue is not a China-Asean problem.

He said the "declaration of conduct" to mitigate tensions in these waters, and related pacts, were products of talks between China and Asean as a group.

Mr Minh also said that while non-claimant states do not take sides on territorial claims, "no member state of Asean or Asean as a group... can or will accept the use of force to change the status quo" by turning undisputed or indisputable areas into disputed ones.