MANILA—It is unconstitutional for President Rodrigo Duterte to be assigned as a special prosecutor to impeach Chief Justice Maria Lourdes Sereno, her camp said on Saturday.

Sereno's spokesperson, lawyer Josalee Deinla, said Duterte cannot participate in impeachment proceedings where he is not involved, "especially since the respondent is the head of a co-equal branch of government."

"Atty. (Larry) Gadon's plan to request Congress to make President Duterte a special prosecutor in the impeachment proceedings against the Chief Justice violates the constitutional role of the House of Representatives to act as sole prosecutors in impeachment cases," Deinla said in a statement.

"Like his impeachment complaint, Mr. Gadon's suggestion is legally infirm. It betrays his fundamental ignorance of the law," it continued.

This, after Gadon on Saturday said he plans to ask Congress to authorize Duterte as a special prosecutor in the impeachment of Sereno.

On Thursday, the House Justice Committee voted 25-2 and declared the impeachment complaint against Sereno sufficient in grounds.

The complaint, filed by Gadon, stemmed from several accusations, including Sereno's alleged non-disclosure of the fees she got from the Piatco case in her 2010 SALN.