Stefan Fule, European commissioner for enlargement, called on Kiev to "address the issues of politically motivated trials, independence of judiciary and selective use of law."
In December, he expressed to Ukrainian leaders his "serious concern" about jailed former Prime Minister Yulia Tymoshenko.
Tymoshenko is serving a seven-year prison sentence after a conviction on charges she abused power when she helped broker a 2009 natural gas deal with Russian energy company Gazprom. Ukrainian officials say the deal created long-term economic problems for the country, though she and her Western allies have said the charges are politically motivated.
European Parliament President Martin Shulz met with visiting Ukrainian Prime Minister Mykola Azarov. Both sides, said Shulz, agreed the European Parliament would send medical experts to Ukraine to visit Tymoshenko.
The former prime minister's health is said to be fragile. She staged a brief hunger strike after saying she was abused by prison authorities.
A "well-respected" person will be sent to Kiev to monitor a second trial for Tymoshenko, said Shulz.
"After an intensive, honest and constructive exchange, we came to common conclusions," he said in a statement. "Prime Minister Azarov answered positively to my two proposals."
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