The results of Ukraine’s snap parliamentary elections were cast into doubt on Monday as attempts by central election officials to count votes faced unexpected delays, prompting Viktor Yushchenko, president, to call for an investigation into possible vote-rigging.

Yulia Tymoshenko, Ukraine’s firebrand opposition leader, and the president’s bloc had claimed victory after exit polls from Sunday’s elections gave them a narrow lead over the governing coalition of prime minister Viktor Yanukovich.