The last Soviet leader Mikhail Gorbachev on Thursday appealed to Russian President Vladimir Putin and U.S. President Barack Obama to broker peace talks to end the deadly violence rocking Ukraine.

"I am sure that you are capable of achieving this aim. The sides fighting each other must sit down together for talks," the 82-year-old statesman said in an open letter published on the website of his Gorbachev Foundation.

"Vladimir Vladimirovich, Mr Obama. I ask you to find the opportunity and take a decisive step to help Ukraine to return to the path of peaceful development," he added, using a respectful form of address to Putin.

Ukraine's anti-government protests escalated into fierce fighting this week that have so far resulted in five deaths and opposition leaders are now in talks with President Viktor Yanukovych demanding concessions including early elections.

Gorbachev warned that the conflict could "threaten not only Ukraine itself and its neighbors but also Europe and the whole world."

"We must not allow Ukrainians to wage war against Ukrainians. That is a terrible absurdity. But the situation seems to have taken such a turn that without help, without the cooperation of the authoritative representatives of our two countries, this could lead to catastrophe," Gorbachev wrote.

In the emotional letter, he described his deep personal links to Ukraine.

"In my family, my mother was Ukrainian while my father was Russian. My late wife Raisa Maximovna was Ukrainian," he said. "We can talk directly of blood links between our people."

Gorbachev is admired in the West for steering his people through the breakup of the Soviet Union, but many Russians blame him for splitting up an empire, and the economic woes of the past two decades in Russia.