A vote scheduled for Ukraine's parliament, on which hangs the fate of both jailed opposition leader Yulia Tymoshenko and Ukraine's EU hopes, has been cancelled.
Attempts to agree a bill that would allow Tymoshenko to leave the country for medical treatment have stalled.
The EU has made the move a condition for it to sign a historic deal on closer ties with Ukraine this month.
But Ukraine has come under intense pressure from Russia not to sign.
Russia wants Ukraine to join its own customs union with Kazakhstan and Belarus, which it sees as a prototype rival to the European Union.
Ukraine's President, Viktor Yanukovych, made a secretive visit to Moscow at the weekend.
MPs said on Wednesday that attempts between the government and opposition to finalise a bill allowing convicts to receive medical treatment abroad had failed.
The bill was meant to allow Tymoshenko to be handed over for medical treatment in Germany.
The former prime minister, and long time bitter rival of President Yanukovych, has been serving a seven-year jail term since being convicted of abuse of power in 2011 over a controversial gas deal with Russia.
Wednesday's parliamentary session was closed without a vote taking place, leading to cries of "Shame!" from the pro-EU opposition.
The speaker said a new session would take place next Tuesday, 19 November. It was unclear whether that would be too late for the EU, as its foreign ministers are scheduled to decide at a meeting on Monday whether the deal with Ukraine can be signed at a summit in Vilnius at the end of the month.
Other bills demanded by the EU, including one on electoral reform, also failed to come to a vote during Wednesday's session.
The parliamentary leader of Tymoshenko's opposition Fatherland group, MP Arseniy Yatsenyuk, blamed the president's ruling Party of the Regions for the failure of the bill, and said it was deliberately trying to destroy the EU deal.
"They are hindering Ukraine's movement towards the European Union," he said.
But the Party of the Regions blamed the opposition for failing to co-operate in talks on the bill.
'Stab in the heart'
Ukrainian and EU negotiators have been working for eight years on the historic association and free trade agreement, which would bestow upon Kiev major benefits such as eventually removing import tariffs.
The pact is a key step on the way to prospective full EU membership.
EU monitors are in Ukraine and were hoping to witness the vote before issuing a progress report on Wednesday night.
The EU has been attempting to build closer relations with neighbours that were once part of the Soviet Union, and is expected to initial but not yet formally sign association agreements with Georgia and Moldova.
Tymoshenko on Tuesday accused President Yanukovych of seeking to undermine the country's EU aspirations.
"Yanukovych wants to convince European leaders that their efforts to protect Ukraine against dictatorship are futile, and they have to give up and retreat," she said in a statement read by her daughter.
And she said the arrest of her own lawyer, Serhiy Vlasenko, on suspicion of domestic violence on Tuesday, was "the last stab" in the heart of closer relations with the EU.
The EU has made clear it believes the judicial campaign against Tymoshenko has been politically motivated.