"Norway is concerned about the treatment of Ukraine's former prime minister Yulia Tymoshenko and the rule of law in the country," Norwegian Foreign Minister Jonas Gahr Støre said in a statement.

"Reports about the treatment of Tymoshenko are worrying. We have asked Ukrainian authorities to immediately shed light on what has happened. Ukraine must live up to its international obligations," he added.

During the meeting with the Ukrainian ambassador, state secretary Torgeir Larsen conveyed Norway's concern not only over the fate of Tymoshenko, but also that of "other political prisoners", and also raised the issue of a proposed Ukrainian law that would ban "propaganda for homosexuality."

"That proposal goes against basic human rights guaranteed by international human rights accords that Ukraine is signatory to," the foreign ministry said.

Tymoshenko, who served as prime minister from late 2007 to early 2010, was jailed for seven years last October on charges of abusing her powers when she was in office when brokering a 2009 gas deal with Russia.

Last month, she launched a hunger strike to protest her alleged beating in jail.