The leader of the Philippine lower house of Congress and a staunch ally of President Rodrigo Duterte on Monday said he was studying whether there was cause to impeach the vice president for her criticism of Duterte's bloody war on drugs.

Duterte himself is facing an impeachment motion, with lower house representative Gary Alejano accusing Duterte of offences ranging from conflict of interest and assets concealment to drugs-related extrajudicial killings and operating a "death squad" during the 22 years he was Davao City mayor.

In a radio interview on Monday, House Speaker Pantaleon Alvarez said he was weighing the possibility of filing an impeachment case against Vice President Leni Robredo for "betrayal of public trust".

Robredo issued a strong rebuke of Duterte's war on drugs last week, describing it in a video sent to the United Nations as an issue of public health that cannot be solved "with bullets alone".

"The act of sending a video clip to the U.N. is really irresponsible," Alvarez said. "This is the first time a high government official has sent a video clip maligning our country. I am looking if this constitutes betrayal of public trust".

A one-third vote in the 292-member lower house of Congress would impeach a high-level official, paving for a Senate trial in which a majority would be needed to remove him or her from office.

Duterte's allies said the impeachment motion against him would be soundly defeated. Duterte has denied wrongdoing.

But political analysts say the impeachment motion was filed against Duterte to show that the justice system in the Philippines does not work, as no court can hold him accountable, other than the International Criminal Court (ICC) in The Hague.

Duterte has welcomed the impeachment complaint, as well as the prospect of the ICC putting him on trial over his war on drugs, saying his campaign would be unrelenting and "brutal".

Source: Timesofoman