The pro-Russian mayor of the eastern Ukrainian town of Kharkiv Gennady Kernes has been taken to hospital after being shot in the spine and wounded in what has been called an assassination attempt, according to Interfax news agency.

Doctors said that Kernes was undergoing surgery, adding that he was in critical condition and fighting for his life. The circumstances of the shooting are still unclear.

Kernes was a supporter of former Ukrainian president Viktor Yanukovich and spoke out against the Maidan revolution that forced him to flee the country.

The development came after heavily armed pro-Russian gunmen seized another city in east Ukraine.

The city of Kostyantynivka is strategically located between the flashpoint town of Slavyansk and the regional hub city of Donetsk, both of which are controlled by rebels.