JOHANNESBURG (AP) — Amnesty International's new leader says his first act is writing to Zimbabwe's next president about the disappearance of activist Itai Dzamara, saying "whoever leads the new government must move to undo the injustices of the past."

Kumi Naidoo, a South African-born former anti-apartheid activist, starts as Amnesty's Secretary General Wednesday. His focus on Dzamara, who disappeared in 2015 under Zimbabwe's former leader Robert Mugabe, puts further pressure on President-elect Emmerson Mnangagwa's government to acknowledge past abuses.

Dzamara is the highest-profile activist to go missing under Mugabe's rule. Last week President Donald Trump signed a law tightening the requirements Zimbabwe must meet for the lifting of U.S. sanctions, which include ordering an inquiry into the disappearance of Dzamara and other rights activists.

Mugabe last month denied knowing of Dzamara's fate.