The Philippine vice-president, Sara Duterte, has threatened to dig up the remains of President Ferdinand Marcos’s dictator father and throw them into the sea, launching a scathing attack on her rival. Duterte was once allied with Marcos Jr, and ran on a joint ticket with him in the 2022 election, winning a landslide victory. However, she resigned from the cabinet in June and the two powerful dynasties are now engaged in a bitter struggle for power before next year’s midterm elections, with both also preparing for presidential polls in 2028. The stakes are especially high for the Dutertes, as the vice-president’s father, the former president Rodrigo Duterte, is facing an investigation by the international criminal court (ICC) for crimes against humanity over his bloody “war on drugs”. In a press conference on Friday, Sara Duterte launched her fiercest attack yet on the president, saying the country was on a “road to hell”, that his administration lacked clear policies to tackle inflation and food security, and that she had once thought about cutting off his head. Duterte said she had been left feeling “used” after teaming up with Marcos before the 2022 election. She realised their relationship had become toxic, she said, after watching him apparently cause the “humiliation” of a young graduate. The graduate had asked Marcos if he could have Marcos’s watch as a graduation gift, only for Marcos to ask him to repeat the question, and then to ask why he should do so, prompting the laughter of those around – and the humiliation of the graduate, she said. “I wanted to remove his head. I realised the relationship was already toxic,” she said. “[I] just imagine myself cutting his head,” she repeated, gesturing with her hands. Tensions between the two rivals have increased after a recent investigation alleging that Duterte has presided over the misuse of public funds, something she has denied, as well as recent parliamentary hearings on the “war on drugs”, which heard claims the office of Rodrigo Duterte paid “rewards” of up to $17,000 to police who killed drugs suspects. Rodrigo Duterte has denied authorising killings. However, he repeatedly and openly threatened drug dealers with death before and during his presidency. Marcos Jr has previously said he would not comply with the ICC’s investigation into the “war on drugs” but analysts say it is possible he could change his stance if he senses his rivals are politically weak. Sara Duterte said if political attacks against her did not stop, she would throw the body of the late dictator Marcos Sr into the sea. “One of these days, I will go there. I will get the body of your father and throw it in the West Philippine Sea,” Duterte said, using the Filipino name for the portion of the South China Sea claimed by Manila. In 2016, when relations between the two families were warm, Rodrigo Duterte caused controversy by allowing a hero’s burial with military honours for Marcos Sr. The late dictator is accused of having plundered up to $10bn from state coffers during his rule, and of presiding over widespread human rights abuses. The presidential communications secretary, Cesar Chavez, said Marcos would not be responding to Sara Duterte’s remarks.