The mayor of Kharkiv in eastern Ukraine has been shot and critically wounded amid continuing unrest in the region.

Hennadiy Kernes was recovering after a two-hour operation to repair damage to the chest and abdomen, but his life remained in danger, his office said.

Monday also saw pro-Russian separatists seize a local government building in Kostyantynivka, a town to the south.

The US has meanwhile expanded sanctions to include targets linked to President Vladimir Putin's "inner circle".

The list includes seven new individuals and 17 companies. The European Union is also expected to announce new sanctions.

Western nations accuse Moscow of supporting separatist gunmen who are occupying official buildings in cities across eastern Ukraine.

The separatists continue to hold seven Western military observers who were seized last week in the region.

Mr Kernes was reportedly out jogging in Kharkiv on Monday when he was shot in the back by an unknown gunman.

The head of the hospital where Mr Kernes is being treated, the Surgery Institute in Kharkiv, said he had suffered a "very serious wound", and that a number of organs had been damaged.

Valeriy Boyko said the threat to the mayor's life had not been eliminated, but that the bleeding had been stopped, his condition was stable and that intensive care doctors were treating him for shock.

Mr Kernes used to be a supporter of the former pro-Moscow President Viktor Yanukovych. He then dropped his support for the ousted president in favour of a united Ukraine.

He has been described as a "mini-oligarch" - a successful businessman wealthy enough to launch a career in politics.

He has been accused of starting his business career as an organised crime boss, a claim he denied while acknowledging that he was once jailed for fraud - a minor offence "partly fabricated" by his enemies, he insisted.

US President Barack Obama confirmed the stepping up of sanctions against Russia, which he said was part of a "calibrated effort" to change Moscow's behaviour in Ukraine, during a visit to the Philippines.

He said the measures were in response to Moscow's failure to uphold an international accord aimed at peacefully resolving the Ukraine crisis.

A White House statement said the new targets were "seven Russian government officials, including two members of President Putin's inner circle, who will be subject to an asset freeze and a US visa ban, and 17 companies linked to Putin's inner circle, which will be subject to an asset freeze".