In a highly unusual move, Prime Minister Stephen Harper publicly rebuked the President of Ukraine Friday over judicial proceedings that led to the imprisonment of his former political opponent Yulia Tymoshenko.

Harper told President Viktor Yanukovych the two countries enjoy a special partnership because of generations of migrations but that the relationship was now strained.

"I am therefore deeply concerned by recent developments in your country, in particular by the apparent political motivation behind the trial of former Prime Minister Yulia Tymoshenko," Harper wrote in a letter that was released to the press.

"The conduct of the Tymoshenko trial, as evaluated by numerous international experts, does not reflect accepted norms of due process of fairness. Canada believes that a fair and independent judiciary is an essential branch of democratic governance," Harper continued.

"I cannot overstate the potential negative impact of the current judicial proceedings against Yulia Tymoshenko both on Ukraine’s future relations with Canada and others, and on Ukraine's long term democratic development.

Our positive bilateral relations since Ukraine’s independence have been built on a shared respect for democracy, human rights and the rule of law," Harper wrote.

Tymoshenko was jailed for seven years early this week for abusing her office, in a trial the United States has suggested was politically motivated and a display of "selective justice."

Then Thursday, Ukraine’s state security service laid new charges against her alleging that Tymoshenko had "conspired" in the 1990s to embezzle government funds from Russian gas exports.

Yumoshenko was a co-leader of the orange revolution, she served as the prime minister of Ukraine and ran for the presidency against Yunkovych in 2010, but lost.

Harper addressed the case during an appearance at the Ukrainian Canadian Congress Friday night. He was also presented with the Shevchenko Medal Award representing the UCC's highest honour.