EU foreign policy chief Federica Mogherini on Thursday urged Russian President Vladimir Putin to make a "radical change" in attitude to end the crisis sparked by Moscow's intervention in Ukraine.

"The fact that Russia is in a difficult situation from a financial point of view is not good news, Mogherini told reporters, referring to the collapse of the Russian ruble, partly due to western sanctions.

"It is not good news for Russian citizens, but also it is not good news for Ukraine, and also it is not good for Europe, or for the rest of the world," she said.

But she added: "President Putin and the Russian leadership should reflect seriously about the need to introduce a radical change in attitude towards the rest of the world, and switch to a cooperative mode," she said.

Mogherini, the former Italian foreign minister, added that the world had "never been as unstable and dangerous as it is now."