"The Verkhovna Rada (parliament) supported my proposal to dismiss Valentyn Nalyvaychenko from his post as head of the SBU," Poroshenko tweeted after 248 lawmakers in the 450-seat chamber supported the president's formal request.
His dismissal highlights the fractured nature of Ukraine's politics and its continued reliance on clan-style alliances and battles that critics say drain attention from far more pressing concerns.
Ukraine's State Security Service enjoys sweeping arrest and domestic surveillance rights it inherited from the domestic branch of the Soviet-era KGB.
He also headed the SBU in 2006-2010 and is believed to have gathered reams of data related to corrupt dealings of both past and present lawmakers and members of government.
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His dismissal comes with Ukraine's 14-month war against pro-Russian insurgents still raging and the economy continuing to implode -- the consequence of years of mismanagement and inability to pass overdue restructuring measures long sought by the International Monetary Fund.
The IMF wanted lawmakers to focus their attention on passing a raft of economic measures that could keep the Fund's USD 17.5-billion rescue for Ukraine in place when its board addresses the issue in early July.
Kiev media reports said Poroshenko had recently tried to move Nalyvaychenko -- seen as a close political ally of former boxer and current Kiev mayor Vitaly Klitschko -- to the foreign intelligence service.
Nalyvaychenko is said to have refused and then launched a political counter-offensive that saw the prosecutor general's office accused of covering up corruption and illegal money making schemes operated by its most senior personnel.
He accused a former deputy prosecutor general of illicitly owning a chain of filling stations whose storage tanker exploded near Kiev last week. The disaster killed five people and set off the region's biggest fire in decades.