Former Prime Minister Yulia Tymoshenko's lawyers say more than 200 pages are missing from a Russian natural-gas contract at the center of her trial in Kyiv.
She is accused of abusing her position by signing the contract in 2009 and faces up to 10 years in prison.
Tymoshenko said the missing pages were evidence the charges were trumped up, lashing out at state prosecutors during her trial on August 29 by accusing them of taking away her right of defense.
"You have not provided access to the materials of the criminal case," Tymoshenko said. "You gave only 1 1/2, two days to review the materials when you had much more than two days."
Prosecutors have denied any pages are missing from Tymoshenko's case files, saying they only appeared to be gone because they had been rearranged after their examination by a state investigator.
Legal specialists say the explanation may be valid. Lawyer Tetyana Montyan told RFE/RL's Ukrainian Service that renumbering pages after their inspection by lawyers is common legal practice in Ukraine.
"There can be more or fewer volumes and the sequence of documents can be altered," Montyan said. "That's not very good, of course, but it's commonly practiced and considered nothing out of the ordinary."
Montyan said Tymoshenko's defense team, which should have its own copies of the pretrial materials, had not proved its accusation so far.
But Tymoshenko lawyer Yuriy Sukhov defended his team's accusations, telling RFE/RL it made copies only of the materials handed over by the court.
"The problem is that we have copies of a letter that states there are 522 additional pages, and another letter regarding 13 additional volumes, but neither the court nor we have those materials," Sukhov said.
Trial Condemned By West, East
Tymoshenko, who has bitterly criticized the trial judge, was jailed earlier this month for contempt of court. The United States and European Union condemned the move and have called for her release.
Her supporters see the trial as a political prosecution by her arch-rival, President Viktor Yanukovych, designed to stop her running in future elections.
Tymoshenko was the heroine of Ukraine's 2004 Orange Revolution, which annulled Yanukovych's victory in a presidential election judges ruled to have been rigged. But Yanukovych bounced back, narrowly defeating Tymoshenko in a presidential race last year.
Although Yanukovych did much to repair Ukraine's tattered relations with Russia, Moscow and Kyiv have been trading barbs over the 2009 gas deal. It raised the price Ukraine pays for gas significantly, but was heralded for normalizing trade ties characterized by yearly disputes and occasional gas shutoffs that affected supplies to many European countries.
Ukrainian Prime Minister Mykola Azarov said on August 30 that Kyiv wanted to discuss changing the agreement, something he said was part of a "regular negotiating process." That appeared to be a change from earlier threats to seek a court ruling to end the contract.
Moscow has criticized Tymoshenko's trial, saying it would not agree to alter the deal.
Yanukovych is expected to be pressured over Tymoshenko's arrest during a visit to Poland, where he is meeting with his Polish counterpart, Boris Komorowski, to discuss relations with the European Union.
Maryana Drach of RFE/RL's Ukrainian Service contributed to this report