A defence lawyer for the imprisoned Ukrainian opposition leader Yulia Tymoshenko has been detained by police, an opposition MP says.
Prosecutors in Kiev are reported to be questioning the lawyer, Serhiy Vlasenko. But Fatherland MP Arseniy Yatsenyuk did not elaborate further.
Ms Tymoshenko, a leader of the 2004 Orange Revolution, is being treated under prison guard for a back injury.
Meanwhile, Ukraine has stopped importing Russian gas, officials say.
Gas has been a thorny issue at the heart of Ukrainian politics for years. Ms Tymoshenko was given her seven-year jail term for abuse of power in 2011 over a controversial gas deal with Russia - a conviction she sees as politically-motivated.
The EU is urging her release as a condition for signing a big trade deal.
The wide-ranging association and free trade agreement with the EU would challenge Ukraine's traditionally close ties with Russia.
The plan is to sign the deal in Lithuania at the end of this month, but the uncertainty about Ms Tymoshenko has fuelled doubt about whether it will go ahead.
In a separate development, Ukraine has stopped importing Russian gas, amid a dispute about Ukrainian payments for gas deliveries.
Ukraine's economy depends on imported Russian gas. The pipelines which run through Ukraine also carry Russian gas to other countries in Eastern and Central Europe.
A Russian energy ministry company managing fuel exports said Ukraine's state energy firm Naftohaz Ukrainy stopped buying gas from Russia's Gazprom on Friday.
A Gazprom official quoted by Reuters news agency said supplies to European clients via Ukraine were unaffected.
There was mid-winter hardship in several European countries in 2006 and 2009 when gas supplies via Ukraine were disrupted.
The Ukrainian government says Naftohaz Ukrainy has paid Gazprom for gas deliveries in October.
But Gazprom director Alexei Miller said last month that Ukraine still owed $882m (£550m) for August deliveries.