Germany on Friday told Ukraine the "window of opportunity" for integration with the European Union could close, as Kiev scrambles to find a solution to the imprisonment of ex-premier Yulia Tymoshenko that has held up an association deal.

German Foreign Minister Guido Westerwelle, wrapping up a two-day visit to Kiev, said he believed Ukraine understood the time pressure as the clock ticks down to a key summit at the end of November.

President Viktor Yanukovych, who met with Westerwelle on his crunch visit, for the first time indicated a solution to the impasse over Tymoshenko could be in sight, without giving details.

"My impression is that all those in Ukraine understand the seriousness of the situation and have recognised the time pressure," Westerwelle said.

"We still have an opened window of opportunity, and it is not to be excluded that this window of opportunity could also once again close."

"There is still a way to go in the political and legal questions that need to be cleared up," said Westerwelle, who on his visit also met Tymoshenko's daughter Yevgenia.

Tymoshenko's continued incarceration risks impeding the signing of an Association Agreement with Brussels at a summit in Vilnius at the end of November, seen as a first step towards Kiev joining the 28-nation bloc.

Westerwelle reaffirmed that an offer to treat Tymoshenko for medical problems in Germany -- a possible solution to the standoff -- remained on the table.

Tymoshenko was sentenced in October 2011 to seven years in jail on abuse of power charges that the EU fears were politically motivated.

Westerwelle said the offer to treat Tymoshenko in Germany had been received "very positively" but gave no hint that his trip had secured an immediate breakthrough.

Tymoshenko, an opposition leader who was a prime protagonist in the 2004 pro-democracy Orange Revolution, contends her jailing was political revenge ordered by Yanukovych to eliminate a dangerous opponent ahead of 2015 presidential polls.

Last week, the special envoys of the European Parliament monitoring mission to Ukraine, Aleksander Kwasniewski and Pat Cox, formally asked Yanukovych to allow Tymoshenko to be taken for treatment outside Ukraine.

In rare comments Friday addressing the issue head on after talks with EU Enlargement Commissioner Stefan Fuele, Yanukovych appeared to indicate that Kiev was aware of the urgency of the issue and a solution could be close.

"We are left so far with the most sensitive issue -- it is the case of Tymoshenko," said Yanukovych.

"But the mission of Cox-Kwasniewski is still working, we are working together, we are looking for ways and I hope that in the near future, we will finally decide in what way to solve this issue."

Sources close to the Ukrainian presidency said Yanukovych was personally handling all exchanges with Cox and Kwasniewski, with discussions held in strict secrecy.

The sources added that it was still unclear if the president had made a final decision on Tymoshenko's fate.

Recent comments by Ukrainian officials have however indicated that the ruling Regions Party could be seeking to rush through parliament legislation that would allow convicts like Tymoshenko to seek medical treatment abroad.

The speaker of the Ukrainian parliament Volodymyr Rybak, a Yanukovych ally, on Friday urged lawmakers from both the ruling party and the opposition to offer a joint bill that would provide a legal basis for Tymoshenko's treatment abroad.

"The authorities and the opposition must work and prepare a law. And we can consider this issue," the parliament speaker said.

Tymoshenko, who is currently receiving medical treatment outside her prison in the city of Kharkiv, has crucially also backed the signing of the Association Agreement and said her fate should not impede the deal.

In an open letter published last week, Tymoshenko said she was ready to accept the offer of treatment in Germany for the sake of a deal in Vilnius, although she still aimed to return to political life and achieve full rehabilitation.

"For the sake of the historic and crucial Agreement with the EU, I am ready to accept such an offer," she said.