[JURIST] A former aide to Ukrainian President Viktor Yushchenko [official website, English version; Wikipedia profile] said Monday that his resignation over the weekend was prompted by corruption within the country's leadership. Former state secretary Oleksandr Zinchenko accused several top presidential aides of corruption, including Petro Poroshenko, who heads the National Security and Defense Council of Ukraine [official website], and Mykola Martynenko, leader of the pro-presidential faction in parliament. Zinchenko said his resignation was meant to "sharply convey this danger to the president and his team." Poroshenko spoke after Zinchenko made his remarks and challenged the former state secretary to come forward with evidence of the alleged corruption, while Martynenko later threatened to sue for libel. Zinchenko's resignation marks the first since Yushchenko assumed the presidency [JURIST report] in January. AP has more.