Ukraine's opposition says a top lawyer for the jailed former Ukrainian Prime Minister Yulia Tymoshenko has been arrested amid strong Western pressure to release Tymoshenko.

Opposition leader Arseniy Yatsenyuk told a parliamentary committee hearing on Monday that he has received a text message from Tymoshenko's attorney Serhiy Vlasenko saying that he has been arrested, according to Yatsenyuk's spokeswoman Olha Lappo.

Tymoshenko's office could not immediately confirm the arrest.