Polish President Bronislaw Komorowski on Sunday was struck by an egg hurled by a young man during a hugely sensitive visit to Ukraine to commemorate a wartime massacre, police said.

The man went up to Komorowski as he was talking to people at a ceremony in the northwestern city of Lutsk to mark the 70th anniversary of the killings of tens of thousands of Poles by Ukrainian nationalists during World War II.

Germany stressed Tuesday that the fate of jailed Ukrainian opposition leader Yulia Tymoshenko would have a decisive impact on Kiev's ambitions for closer ties with the European Union.

Foreign Minister Guido Westerwelle told reporters after talks with his Ukrainian counterpart Leonid Kozhara that negotiations were ongoing to secure Ukrainian permission for the ailing Tymoshenko to receive medical treatment in Germany.

The daughter of jailed Ukrainian opposition leader Yulia Tymoshenko said Monday that German doctors had determined her ailing mother was in urgent need of surgery on her back.

She said the doctors, who in recent months have visited the firebrand former 2004 pro-democracy Orange Revolution leader, had concluded that Tymoshenko's health was deteriorating.

Germany is in talks with Ukraine on an offer to treat jailed former prime minister Yulia Tymoshenko for her health problems in Berlin, Foreign Minister Guido Westerwelle said Friday.

"The German offer of medical treatment for Mrs Tymoshenko in Berlin remains in place. I emphasized this," Westerwelle told reporters after meeting Ukrainian President Viktor Yanukovych in Kiev.

Ukrainian opposition leader Yulia Tymoshenko's daughter Yevgenia on Monday warned that her mother's health is worsening, after a rare visit to her hospital bedside.

"On Friday she got worse during a therapy session... and now she feels very sharp pain with almost any movement despite taking a strong painkiller," Yevgenia Tymoshenko told reporters in the eastern Ukrainian city of Kharkiv where Tymoshenko is serving her sentence.

The European Court of Human Rights ruled Tuesday that Ukraine's detention of former Prime Minister Yulia Tymoshenko was unlawful, in a decision the opposition leader's camp saw as a key step towards her release.

Tymoshenko herself said she hoped the decision by the Strasbourg-based court would put paid to the "dirt and black lies" against her.

Ukrainians on Friday lit candles and laid flowers to remember the victims of the world's worst nuclear disaster at Chernobyl 27 years ago, as engineers pressed on with efforts to construct a new shelter to permanently secure the stricken reactor.

An explosion during testing in the early hours of April 26, 1986, sent radioactive fallout into the atmosphere that spread across Europe, particularly contaminating Belarus, Ukraine and Russia.

Opposition lawmakers in the Ukrainian parliament on Friday called for the release of jailed ex-prime minister Yulia Tymoshenko and for the dismissal of the government of her bitter foe President Viktor Yanukovych.

"Our political demand is the release of Yulia Tymoshenko and her return to political life," said prominent opposition leader Arseniy Yatsenyuk, as his supporters chanted "Free Yulia!"

Ukraine's high court on Wednesday rejected an appeal by former interior minister Yuriy Lutsenko, a close ally of jailed opposition leader Yulia Tymoshenko, against his four-year jail term for abuse of office and embezzlement.

The High Specialized Court of Ukraine confirmed the sentence, meaning that Lutsenko, who has complained of health problems, will stay in prison until the end of December 2014, an Agence France Presse correspondent reported.

Over 5,000 people led by opposition leaders like boxing star Vitaly Klitschko took to the streets of Kiev Tuesday to protest against city authorities and demand mayoral elections.

The Ukrainian capital's previous mayor Leonid Chernovetsky, who bewildered Ukrainians with his bizarre antics and was accused of insanity by opponents, resigned last year.