Ukrainian President Viktor Yushchenko (search) fired his government Thursday, saying the abrupt action was motivated by an absence of team spirit among Cabinet members and other top aides.

Prime Minister Yulia Tymoshenko's (search) fragile coalition of former opposition leaders fell amid the greatest crisis to face Yushchenko in his seven months in power.

Yushchenko appointed lawmaker Yuriy Yekhanurov (search), a former economics minister who now heads a parliamentary committee on industrial issues, as acting prime minister.

Yushchenko also accepted the resignation of Petro Poroshenko, the head of the Security and Defense Council (search), and parliament quickly voted to strip him of his legislative seat. Poroshenko stepped down Thursday after two other high-level officials quit, accusing him of corruption.

Yushchenko had spent the past three days huddled in meetings with Poroshenko and Tymoshenko, reportedly trying to find a way out of the crisis.

Earlier Thursday, Vice Prime Minister Mykola Tomenko became the second top official to step down in a week, accusing Poroshenko and others of corruption.

"I have realized that some people steal and others resign," Tomenko, who left his post in charge of humanitarian affairs, told a news conference in Kiev. "I don't want to bear common responsibility for people who have created a corrupt system."

Yushchenko's chief-of-staff, Oleksandr Zinchenko, resigned Saturday and also leveled charges of corruption against high-level officials, including Poroshenko.

Late Wednesday, Yushchenko said personal conflicts between members of the government "cause serious damage not only to the team's reputation, but also to the government's image," according to his office. "Responsibility for this lies with everyone."