Ukraine's jailed former prime minister is ready to urge the European Union to drop the demand for her release if it could help persuade the government to sign a landmark association agreement, her lawyer said.

Yulia Tymoshenko, who is considered by the West to be a political prisoner, also urged Ukrainians on Friday to take to the streets to protest the government's decision to shelve the deal and turn to Russia instead.

An EU spokeswoman said Ukraine's President Viktor Yanukovych was still welcome to attend the summit next week in Vilnius that offers the country a chance to sign a free trade and political association agreement with the bloc on condition of Tymoshenko's release.

"Our firm belief is that the future of Ukraine still lies in a strong relationship with the EU," Maja Kocijancic, spokeswoman for the European Union's top diplomat, Catherine Ashton, said.

Derailing EU-Ukraine deal

Ukraine's Cabinet on Thursday suspended preparations for signing the agreement in what was seen as a major victory for Russia, which has worked aggressively to derail the deal and keep Ukraine in its orbit.

Prime Minister Mykola Azarov tried to defend the decision in parliament on Friday, but was booed by opposition lawmakers, who chanted "Shame!" and threw stacks of papers at his ministers.

Azarov said Ukraine cannot afford to lose trade with Russia and suggested the EU did not offer Ukraine any compensation for that. He also complained that the conditions the International Monetary Fund has set for rescuing its struggling economy with a bailout loan were impossible to fulfill.

Arseniy Yatsenyuk, Tymoshenko's top ally, accused Yanukovych of selling out to Moscow in exchange for cash and ensuring his re-election in 2015.

"This is a well-planned scenario by Yanukovych: how to sell the Ukrainian state and to buy himself a seat of the governor of Little Russia as part of the great Russian empire," Yatsenyuk said.

Russia's President Vladimir Putin, speaking in St Petersburg on Friday, denied twisting Ukraine's arm, and, in turn, accused the EU of "pressure and blackmail".

"It will become clear in the next few days whether Ukraine and its leadership will yield to pressure or will be able to resist it and take a pragmatic stance in line with national interests," Putin said.

Protesters call for EU deal

Yatsenyuk called on Ukrainians to join an opposition rally on Sunday on Kiev's central square.

A smaller protest was already underway there. Several dozen activists wrapped in the yellow-and-blue Ukrainian flags hid from rain under umbrellas.

"Europe is our future. In Europe a person is treated with respect," said Vitaliy Tokaryuk, 25, a real estate agent who had spent the night on the Independence Square.

Sunday's rally will test the strength of the opposition, and some say that a large showing may nudge Yanukovych back in the direction of the EU.