MANILA (Reuters) - A Philippines lawmaker filed supplementary charges on Thursday to an impeachment complaint against President Rodrigo Duterte, accusing him of taking a “defeatist stance” by doing nothing to challenge Beijing’s activities in the South China Sea.

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Opposition congressman Gary Alejano said Duterte had made a slew of remarks that proved he had no intention to protect Philippine sovereignty and had alienated key allies like the United States through “rants and unstoppable outbursts”.

The complaint adds to a laundry list of what Alejano says are impeachable offences that amount to high crimes, abuse of power and betrayal of public trust.

He submitted the initial complaint two weeks ago, just as Congress went into a recess, a move aimed at keeping it in the public spotlight and preventing Congress from dismissing it right away. It reconvenes on May 2.

Duterte is frequently accused of abuse of power, though none of the allegations have so far stuck. The populist former city mayor commands a legislative majority and enjoys huge public support.

Presidential Legal Counsel Salvador Panelo said Alejano’s additional complaint was groundless propaganda and part of a coordinated conspiracy by Duterte’s opponents.

Alejano said Duterte had failed to act on a ruling by the Permanent Court of Arbitration last year that invalidated China’s nine-dash line claim to most of the South China Sea, its justification for building man-made islands in Manila’s exclusive economic zone.

He said Duterte’s recent comments that he could do nothing to stop China if it were to build structures at the disputed Scarborough Shoal indicated his unwillingness to defend the country’s rights.

The criticism comes as Duterte intensifies his charm offensive to encourage China to invest billions of dollars in the Philippines, including its flagging infrastructure, an approach that contrasts sharply with his open hostility towards the United States.

He last week railed against Washington for allowing China to construct and arm its artificial islands, but placed no blame on Beijing.

On Wednesday Duterte said he had asked the U.S. ambassador to Manila “why did you not send the armada?”.

A U.S. think-tank on Monday said China had finished building military infrastructure on those islands and was now capable of deploying combat planes there.