"The German offer of medical treatment for Mrs Tymoshenko in Berlin remains in place. I emphasised this," Westerwelle told reporters after meeting Ukrainian President Viktor Yanukovych in Kiev.
"We will work together towards a good solution. Time will tell if this is possible. But it is important news that we are working on this and will continue to work on this," he added.
The seven-year jail term handed to Tymoshenko on abuse of power charges in 2011 has severely harmed Ukraine's relations with the European Union and is holding up the signing of an Association Agreement with the bloc.
Ukraine has sets its sights on joining the European Union and such an agreement would be a first formal step on the road to membership.
Tymoshenko is currently in hospital outside of her jail in the city of Kharkiv where she is receiving treatment on a herniated disc which supporters say is giving her chronic pain.
Westerwelle described his talks with Yanukovych as "constructive" but said that Kiev needed to remove the "obstacles" on the way to its closer integration with the European Union.
"Every semblance of selective justice should be removed," said Westerwelle.
"I emphasised to Mr President that once again we are pressing for a solution to the Tymoshenko case," said Westerwelle. The top German diplomat declined to give details on the president's response to the German offer of treating her in Berlin.
However Tymoshenko's political ally Arseniy Yatsenyuk said this week that Yanukovych had told him and other party leaders that Kiev was discussing with its Western partners the possibility of sending her abroad for treatment.