MANILA (REUTERS) - Philippine President Rodrigo Duterte on Thursday (Dec 8) vowed to retain the country's vice-president until her term ends, just days after she resigned from the Cabinet, complaining of a "plot to steal" her position.

Vice-President Leni Robredo resigned from the Cabinet on Monday, saying she would lead the opposition and challenge Mr Duterte's policies, such as his deadly war on drugs and moves to reinstate the death penalty.

"I will assure Leni and the rest of the Bicol region that you will have her until the very end of this term," Mr Duterte told reporters after a ceremony to break ground for an airport in the central region of Bicol. "And there is no such thing as removing a vice-president."

Ms Robredo was a one-term congresswoman from Naga City, located in Bicol.

In earlier speeches, Mr Duterte has accused the opposition of using street protests against the burial of the late dictator Ferdinand Marcos in a heroes' cemetery as a pretext to force him out of office and make way for Ms Robredo.

Ms Robredo was elected vice-president in May in a separate contest and was not Mr Duterte's running mate. Mr Alan Peter Cayetano was Mr Duterte's running mate.

Ms Robredo has warned of a plot taking shape to remove her from the number two post after she was barred from attending regular Cabinet meetings.

The 52-year-old social activist and human rights lawyer won by a narrow margin over former senator Ferdinand Marcos Jr, whose father was overthrown in a 1986 revolt. He has filed an election protest.

Ms Robredo did not give details of the alleged plot to "steal" the vice-presidency, but said it was telling that Mr Ferdinand Marcos Jr had accompanied Mr Duterte on an official visit to China in October.