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MANILA - The appointment of Vice President Leni Robredo as co-chair of government's committee against illegal drugs is a "ladder to the presidency," Malacañang said Tuesday.

• Duterte designates Robredo as co-chair of committee vs illegal drugs

President Rodrigo Duterte's appointment of Robredo is a "a sincere gesture and a challenge," according to his spokesman Salvador Panelo, who said the Vice President is "welcome in the Cabinet."

The opposition had cast doubts on Duterte's drug czar offer to Robredo, with detained Sen. Leila de Lima saying it was a "silly trap."

• De Lima believes ‘drug czar’ offer to Robredo a ‘trap’ meant to ‘shame’ VP

Panelo, however, said Robredo should not listen to her colleagues "who don’t want her to succeed."

"We’re giving her a ladder to the presidency, this is her chance, this is her moment. She should accept it. Be in the moment, help the Filipino people, help this country and help herself. And show her colleagues that she can do it," he told ANC.

Last month, Robredo had called on Duterte to allow the United Nations to investigate his war on drugs which she said was “obviously, not working,” prompting Malacanang's challenge for her to lead the drug war.

• Robredo on Duterte's drug czar offer: 'Kung walang failure, bakit ipapasa sa akin?'

Panelo said Duterte has ordered all state agencies to "support and cooperate" with Robredo as co-chair of the Inter-Agency Committee on Anti-Illegal Drugs until the President steps down on June 30, 2022.

"It will be a good working relationship. In fact since the President's giving the blanket authority of co-chair then she can do everything she wants with the President supporting her," he said.

"You must remember that the success of this Vice President will be the success of all of us."