Ukrainian President and honorary member of the Party of Regions of Ukraine Viktor Yanukovych arrived in Kharkiv in the early hours of Saturday, a source with knowledge of the situation told Interfax.

Yanukovych is supposed to take part in a congress of lawmakers from southeastern regions of Ukraine on Saturday, he said.

"This is what is planned, but the situation is changing rapidly. Changes are possible," the source said.

A high-ranking source from Yanukovych's entourage had said earlier in an interview with the Dzerkalo Tyzhnia (Mirror Weekly, ZN.UA) that Yanukovych, accompanied by a narrow circle of especially trusted security guards, had flown to Kharkiv from Kyiv at 10:40 p.m. without stopping over at the suburban presidential residence of Mezhyhirya.

The source said Verkhovna Rada Chairman Volodymyr Rybak and presidential chief of staff Andriy Kliuyev were on the same plane with Yanukovych.

"The plane's supposed route is Kyiv-Kharkiv-Mariupol-the Russian Federation, but the route may be adjusted," the online version of ZN.UA said.

The source said also that Yanukovych doubted whether it was appropriate to sign legislation on reinstating the 2004 constitution passed by the Verkhovna Rada on Friday.

Kharkiv is to host a congress of lawmakers of all levels from the southeastern regions of Ukraine, Sevastopol, and the autonomous republic of Crimea on Saturday.